diff --git a/core/txpool/errors.go b/core/txpool/errors.go
index 855b52c818..7b03d80e88 100644
--- a/core/txpool/errors.go
+++ b/core/txpool/errors.go
@@ -71,5 +71,7 @@ var (
 
 	ErrDuplicateSpecialTransaction = errors.New("duplicate a special transaction")
 
+	ErrSpecialTxCostOverflow = errors.New("special transaction cost overflow")
+
 	ErrMinDeploySMC = errors.New("smart contract creation cost is under allowance")
 )
diff --git a/core/txpool/legacypool/legacypool.go b/core/txpool/legacypool/legacypool.go
index 4c9aab066c..305f35dec7 100644
--- a/core/txpool/legacypool/legacypool.go
+++ b/core/txpool/legacypool/legacypool.go
@@ -1072,17 +1072,38 @@ func (pool *LegacyPool) promoteTx(addr common.Address, hash common.Hash, tx *typ
 }
 
 func (pool *LegacyPool) promoteSpecialTx(addr common.Address, tx *types.Transaction, isLocal bool) (bool, error) {
-	// Try to insert the transaction into the pending queue
-	if pool.pending[addr] == nil {
-		pool.pending[addr] = newList(true)
+	list := pool.pending[addr]
+	newPending := list == nil
+	if newPending {
+		list = newList(true)
+	}
+
+	base := new(uint256.Int).Set(list.totalcost)
+	old := list.txs.Get(tx.Nonce())
+	if old != nil {
+		if old.IsSpecialTransaction() {
+			return false, txpool.ErrDuplicateSpecialTransaction
+		}
+		// Old is being replaced, subtract old cost
+		if _, underflow := base.SubOverflow(base, uint256.MustFromBig(old.Cost())); underflow {
+			panic("totalcost underflow")
+		}
+	}
+	// Keep overflow behavior aligned with list.Add.
+	cost, overflow := uint256.FromBig(tx.Cost())
+	if overflow {
+		return false, txpool.ErrSpecialTxCostOverflow
+	}
+	total, overflow := new(uint256.Int).AddOverflow(base, cost)
+	if overflow {
+		return false, txpool.ErrSpecialTxCostOverflow
+	}
+	list.totalcost = total
+	if newPending {
+		pool.pending[addr] = list
 		pendingAddrsGauge.Inc(1)
 	}
-	list := pool.pending[addr]
 
-	old := list.txs.Get(tx.Nonce())
-	if old.IsSpecialTransaction() {
-		return false, txpool.ErrDuplicateSpecialTransaction
-	}
 	// Otherwise discard any previous transaction and mark this
 	if old != nil {
 		pool.all.Remove(old.Hash())
@@ -1093,7 +1114,7 @@ func (pool *LegacyPool) promoteSpecialTx(addr common.Address, tx *types.Transact
 		pendingGauge.Inc(1)
 	}
 	list.txs.Put(tx)
-	if cost := uint256.MustFromBig(tx.Cost()); list.costcap.Cmp(cost) < 0 {
+	if cost := tx.Cost(); list.costcap.Cmp(cost) < 0 {
 		list.costcap = cost
 	}
 	if gas := tx.Gas(); list.gascap < gas {
@@ -1648,7 +1669,7 @@ func (pool *LegacyPool) promoteExecutables(accounts []common.Address) []*types.T
 		if pool.chain.CurrentHeader() != nil {
 			number = pool.chain.CurrentHeader().Number
 		}
-		drops, _ := list.Filter(uint256.MustFromBig(pool.currentState.GetBalance(addr)), gasLimit, pool.trc21FeeCapacity, number)
+		drops, _ := list.Filter(pool.currentState.GetBalance(addr), gasLimit, pool.trc21FeeCapacity, number)
 		for _, tx := range drops {
 			pool.all.Remove(tx.Hash())
 		}
@@ -1853,7 +1874,7 @@ func (pool *LegacyPool) demoteUnexecutables() {
 		if pool.chain.CurrentHeader() != nil {
 			number = pool.chain.CurrentHeader().Number
 		}
-		drops, invalids := list.Filter(uint256.MustFromBig(pool.currentState.GetBalance(addr)), gasLimit, pool.trc21FeeCapacity, number)
+		drops, invalids := list.Filter(pool.currentState.GetBalance(addr), gasLimit, pool.trc21FeeCapacity, number)
 		for _, tx := range drops {
 			hash := tx.Hash()
 			pool.all.Remove(hash)
diff --git a/core/txpool/legacypool/legacypool_test.go b/core/txpool/legacypool/legacypool_test.go
index c80e2f305d..c7adc7fe8d 100644
--- a/core/txpool/legacypool/legacypool_test.go
+++ b/core/txpool/legacypool/legacypool_test.go
@@ -272,6 +272,173 @@ func deriveSender(tx *types.Transaction) (common.Address, error) {
 	return types.Sender(types.HomesteadSigner{}, tx)
 }
 
+func TestPromoteSpecialTxUpdatesTotalCost(t *testing.T) {
+	pool, key := setupPool()
+	defer pool.Close()
+
+	normal := transaction(0, 21000, key)
+	addr, err := deriveSender(normal)
+	if err != nil {
+		t.Fatalf("failed to derive sender: %v", err)
+	}
+	special := setCodeTx(0, key, nil)
+
+	pool.mu.Lock()
+	defer pool.mu.Unlock()
+
+	pool.pending[addr] = newList(true)
+	list := pool.pending[addr]
+
+	inserted, _ := list.Add(normal, pool.config.PriceBump)
+	if !inserted {
+		t.Fatal("failed to insert baseline transaction")
+	}
+	if _, err := pool.promoteSpecialTx(addr, special, false); err != nil {
+		t.Fatalf("promoteSpecialTx failed: %v", err)
+	}
+	want, overflow := uint256.FromBig(special.Cost())
+	if overflow {
+		t.Fatal("special tx cost overflowed uint256 in test setup")
+	}
+	if list.totalcost.Cmp(want) != 0 {
+		t.Fatalf("totalcost mismatch after special promotion: have %v want %v", list.totalcost, want)
+	}
+
+	// Removing the pending tx should not underflow totalcost.
+	list.Forward(1)
+	if list.totalcost.Sign() != 0 {
+		t.Fatalf("totalcost should be zero after removal, have %v", list.totalcost)
+	}
+}
+
+func TestListAddReplacementAvoidsIntermediateOverflow(t *testing.T) {
+	key, err := crypto.GenerateKey()
+	if err != nil {
+		t.Fatalf("failed to generate key: %v", err)
+	}
+	max := new(big.Int).Sub(new(big.Int).Lsh(common.Big1, 256), common.Big1)
+	oldPrice := new(big.Int).Sub(new(big.Int).Rsh(new(big.Int).Set(max), 1), big.NewInt(100))
+	newPrice := new(big.Int).Add(oldPrice, common.Big1)
+
+	oldTx, err := types.SignTx(types.NewTransaction(0, common.Address{}, common.Big0, 1, oldPrice, nil), types.HomesteadSigner{}, key)
+	if err != nil {
+		t.Fatalf("failed to sign old tx: %v", err)
+	}
+	newTx, err := types.SignTx(types.NewTransaction(0, common.Address{}, common.Big0, 1, newPrice, nil), types.HomesteadSigner{}, key)
+	if err != nil {
+		t.Fatalf("failed to sign replacement tx: %v", err)
+	}
+
+	list := newList(true)
+	inserted, _ := list.Add(oldTx, 0)
+	if !inserted {
+		t.Fatal("failed to insert baseline transaction")
+	}
+	inserted, replaced := list.Add(newTx, 0)
+	if !inserted {
+		t.Fatal("replacement transaction should not overflow after subtracting old cost")
+	}
+	if replaced == nil || replaced.Hash() != oldTx.Hash() {
+		t.Fatal("expected old transaction to be replaced")
+	}
+	want, overflow := uint256.FromBig(newTx.Cost())
+	if overflow {
+		t.Fatal("replacement tx cost overflowed uint256 in test setup")
+	}
+	if list.totalcost.Cmp(want) != 0 {
+		t.Fatalf("totalcost mismatch after replacement: have %v want %v", list.totalcost, want)
+	}
+	if tx := list.txs.Get(newTx.Nonce()); tx == nil || tx.Hash() != newTx.Hash() {
+		t.Fatal("replacement transaction was not stored in list")
+	}
+	list.Forward(1)
+	if list.totalcost.Sign() != 0 {
+		t.Fatalf("totalcost should be zero after removal, have %v", list.totalcost)
+	}
+}
+
+func TestPromoteSpecialTxReplacementAvoidsIntermediateOverflow(t *testing.T) {
+	pool, key := setupPool()
+	defer pool.Close()
+
+	max := new(big.Int).Sub(new(big.Int).Lsh(common.Big1, 256), common.Big1)
+	oldPrice := new(big.Int).Sub(new(big.Int).Rsh(new(big.Int).Set(max), 1), big.NewInt(100))
+	newPrice := new(big.Int).Add(oldPrice, common.Big1)
+	oldTx, err := types.SignTx(types.NewTransaction(0, common.Address{}, common.Big0, 1, oldPrice, nil), types.HomesteadSigner{}, key)
+	if err != nil {
+		t.Fatalf("failed to sign old tx: %v", err)
+	}
+	addr, err := deriveSender(oldTx)
+	if err != nil {
+		t.Fatalf("failed to derive sender: %v", err)
+	}
+	special := pricedSetCodeTx(0, 1, uint256.MustFromBig(newPrice), uint256.NewInt(1), key, nil)
+
+	pool.mu.Lock()
+	defer pool.mu.Unlock()
+
+	pool.pending[addr] = newList(true)
+	list := pool.pending[addr]
+	inserted, _ := list.Add(oldTx, 0)
+	if !inserted {
+		t.Fatal("failed to insert baseline transaction")
+	}
+	inserted, err = pool.promoteSpecialTx(addr, special, false)
+	if err != nil {
+		t.Fatalf("promoteSpecialTx failed: %v", err)
+	}
+	if !inserted {
+		t.Fatal("special replacement should not overflow after subtracting old cost")
+	}
+	want, overflow := uint256.FromBig(special.Cost())
+	if overflow {
+		t.Fatal("special tx cost overflowed uint256 in test setup")
+	}
+	if list.totalcost.Cmp(want) != 0 {
+		t.Fatalf("totalcost mismatch after special replacement: have %v want %v", list.totalcost, want)
+	}
+	if tx := list.txs.Get(special.Nonce()); tx == nil || tx.Hash() != special.Hash() {
+		t.Fatal("special replacement transaction was not stored in list")
+	}
+	list.Forward(1)
+	if list.totalcost.Sign() != 0 {
+		t.Fatalf("totalcost should be zero after removal, have %v", list.totalcost)
+	}
+}
+
+func TestPromoteSpecialTxOverflowReturnsErrorWithoutMutation(t *testing.T) {
+	pool, key := setupPool()
+	defer pool.Close()
+
+	normal := transaction(0, 21000, key)
+	addr, err := deriveSender(normal)
+	if err != nil {
+		t.Fatalf("failed to derive sender: %v", err)
+	}
+	max := new(big.Int).Sub(new(big.Int).Lsh(common.Big1, 256), common.Big1)
+	special := pricedSetCodeTx(0, 2, uint256.MustFromBig(max), uint256.NewInt(1), key, nil)
+
+	pool.mu.Lock()
+	defer pool.mu.Unlock()
+
+	inserted, err := pool.promoteSpecialTx(addr, special, false)
+	if inserted {
+		t.Fatal("overflowing special tx must not be inserted")
+	}
+	if !errors.Is(err, txpool.ErrSpecialTxCostOverflow) {
+		t.Fatalf("wrong error: have %v, want %v", err, txpool.ErrSpecialTxCostOverflow)
+	}
+	if _, ok := pool.pending[addr]; ok {
+		t.Fatal("pending list created for rejected special tx")
+	}
+	if pool.all.Get(special.Hash()) != nil {
+		t.Fatal("rejected special tx should not be tracked in lookup")
+	}
+	if pool.pendingNonces.get(addr) != 0 {
+		t.Fatalf("pending nonce changed for rejected special tx: have %d want 0", pool.pendingNonces.get(addr))
+	}
+}
+
 type testChain struct {
 	*testBlockChain
 	address common.Address
diff --git a/core/txpool/legacypool/list.go b/core/txpool/legacypool/list.go
index 0faad824d7..9461bc324e 100644
--- a/core/txpool/legacypool/list.go
+++ b/core/txpool/legacypool/list.go
@@ -274,7 +274,7 @@ type list struct {
 	strict bool       // Whether nonces are strictly continuous or not
 	txs    *sortedMap // Heap indexed sorted hash map of the transactions
 
-	costcap   *uint256.Int // Price of the highest costing transaction (reset only if exceeds balance)
+	costcap   *big.Int     // Price of the highest costing transaction (reset only if exceeds balance)
 	gascap    uint64       // Gas limit of the highest spending transaction (reset only if exceeds block limit)
 	totalcost *uint256.Int // Total cost of all transactions in the list
 }
@@ -285,7 +285,7 @@ func newList(strict bool) *list {
 	return &list{
 		strict:    strict,
 		txs:       newSortedMap(),
-		costcap:   new(uint256.Int),
+		costcap:   new(big.Int),
 		totalcost: new(uint256.Int),
 	}
 }
@@ -302,12 +302,13 @@ func (l *list) Contains(nonce uint64) bool {
 // If the new transaction is accepted into the list, the lists' cost and gas
 // thresholds are also potentially updated.
 func (l *list) Add(tx *types.Transaction, priceBump uint64) (bool, *types.Transaction) {
+	base := new(uint256.Int).Set(l.totalcost)
 	// If there's an older better transaction, abort
 	old := l.txs.Get(tx.Nonce())
-	if old.IsSpecialTransaction() {
-		return false, nil
-	}
 	if old != nil {
+		if old.IsSpecialTransaction() {
+			return false, nil
+		}
 		if old.GasFeeCapCmp(tx) >= 0 || old.GasTipCapCmp(tx) >= 0 {
 			return false, nil
 		}
@@ -328,18 +329,24 @@ func (l *list) Add(tx *types.Transaction, priceBump uint64) (bool, *types.Transa
 			return false, nil
 		}
 		// Old is being replaced, subtract old cost
-		l.subTotalCost([]*types.Transaction{old})
+		if _, underflow := base.SubOverflow(base, uint256.MustFromBig(old.Cost())); underflow {
+			panic("totalcost underflow")
+		}
 	}
 	// Add new tx cost to totalcost
 	cost, overflow := uint256.FromBig(tx.Cost())
 	if overflow {
 		return false, nil
 	}
-	l.totalcost.Add(l.totalcost, cost)
+	total, overflow := new(uint256.Int).AddOverflow(base, cost)
+	if overflow {
+		return false, nil
+	}
+	l.totalcost = total
 
 	// Otherwise overwrite the old transaction with the current one
 	l.txs.Put(tx)
-	if l.costcap.Cmp(cost) < 0 {
+	if cost := tx.Cost(); l.costcap.Cmp(cost) < 0 {
 		l.costcap = cost
 	}
 	if gas := tx.Gas(); l.gascap < gas {
@@ -366,12 +373,12 @@ func (l *list) Forward(threshold uint64) types.Transactions {
 // a point in calculating all the costs or if the balance covers all. If the threshold
 // is lower than the costgas cap, the caps will be reset to a new high after removing
 // the newly invalidated transactions.
-func (l *list) Filter(costLimit *uint256.Int, gasLimit uint64, trc21Issuers map[common.Address]*big.Int, number *big.Int) (types.Transactions, types.Transactions) {
+func (l *list) Filter(costLimit *big.Int, gasLimit uint64, trc21Issuers map[common.Address]*big.Int, number *big.Int) (types.Transactions, types.Transactions) {
 	// If all transactions are below the threshold, short circuit
 	if l.costcap.Cmp(costLimit) <= 0 && l.gascap <= gasLimit {
 		return nil, nil
 	}
-	l.costcap = new(uint256.Int).Set(costLimit) // Lower the caps to the thresholds
+	l.costcap = new(big.Int).Set(costLimit) // Lower the caps to the thresholds
 	l.gascap = gasLimit
 
 	// Filter out all the transactions above the account's funds
@@ -379,10 +386,10 @@ func (l *list) Filter(costLimit *uint256.Int, gasLimit uint64, trc21Issuers map[
 		maximum := costLimit
 		if tx.To() != nil {
 			if feeCapacity, ok := trc21Issuers[*tx.To()]; ok {
-				return tx.Gas() > gasLimit || new(big.Int).Add(costLimit.ToBig(), feeCapacity).Cmp(tx.TxCost(number)) < 0
+				return tx.Gas() > gasLimit || new(big.Int).Add(costLimit, feeCapacity).Cmp(tx.TxCost(number)) < 0
 			}
 		}
-		return tx.Gas() > gasLimit || tx.Cost().Cmp(maximum.ToBig()) > 0
+		return tx.Gas() > gasLimit || tx.Cost().Cmp(maximum) > 0
 	})
 
 	if len(removed) == 0 {
diff --git a/core/txpool/legacypool/list_test.go b/core/txpool/legacypool/list_test.go
index 5a6b9af466..cf54eefe23 100644
--- a/core/txpool/legacypool/list_test.go
+++ b/core/txpool/legacypool/list_test.go
@@ -24,7 +24,6 @@ import (
 	"github.com/XinFinOrg/XDPoSChain/common"
 	"github.com/XinFinOrg/XDPoSChain/core/types"
 	"github.com/XinFinOrg/XDPoSChain/crypto"
-	"github.com/holiman/uint256"
 )
 
 // Tests that transactions can be added to strict lists and list contents and
@@ -78,7 +77,7 @@ func BenchmarkListAdd(t *testing.B) {
 	}
 	// Insert the transactions in a random order
 	list := newList(true)
-	priceLimit := uint256.NewInt(DefaultConfig.PriceLimit)
+	priceLimit := big.NewInt(int64(DefaultConfig.PriceLimit))
 	t.ResetTimer()
 	for _, v := range rand.Perm(len(txs)) {
 		list.Add(txs[v], DefaultConfig.PriceBump)