diff --git a/portalnetwork/history/accumulator.go b/portalnetwork/history/accumulator.go
index 9dafee13c231..56f7028f9956 100644
--- a/portalnetwork/history/accumulator.go
+++ b/portalnetwork/history/accumulator.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/portalnetwork/utils"
 	"github.com/ethereum/go-ethereum/rlp"
 	ssz "github.com/ferranbt/fastssz"
 	"github.com/holiman/uint256"
@@ -43,11 +44,15 @@ func newEpoch() *epoch {
 
 func (e *epoch) add(header types.Header) error {
 	blockHash := header.Hash().Bytes()
-	difficulty := uint256.MustFromBig(header.Number)
+	difficulty := uint256.MustFromBig(header.Difficulty)
 	e.difficulty = uint256.NewInt(0).Add(e.difficulty, difficulty)
+	// big-endian
+	difficultyBytes := e.difficulty.Bytes32()
+	utils.ReverseBytesInPlace(difficultyBytes[:])
+
 	record := HeaderRecord{
 		BlockHash:       blockHash,
-		TotalDifficulty: e.difficulty.Bytes(),
+		TotalDifficulty: difficultyBytes[:],
 	}
 	sszBytes, err := record.MarshalSSZ()
 	if err != nil {
diff --git a/portalnetwork/history/accumulator_test.go b/portalnetwork/history/accumulator_test.go
index 0df94fe78ccb..9d66a06b3a1e 100644
--- a/portalnetwork/history/accumulator_test.go
+++ b/portalnetwork/history/accumulator_test.go
@@ -4,13 +4,16 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"math/big"
 	"os"
 	"strconv"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/portalnetwork/utils"
 	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/holiman/uint256"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -51,6 +54,35 @@ func TestBuildAndVerifyProof(t *testing.T) {
 	}
 }
 
+func TestUpdate(t *testing.T) {
+	epochAcc, err := getEpochAccu("0xcddbda3fd6f764602c06803ff083dbfc73f2bb396df17a31e5457329b9a0f38d")
+	assert.NoError(t, err)
+
+	startNumber := 1000000
+	epochRecordIndex := GetHeaderRecordIndex(uint64(startNumber))
+
+	newEpochAcc := NewAccumulator()
+
+	for i := 0; i <= int(epochRecordIndex); i++ {
+		tmp := make([]byte, 64)
+		copy(tmp, epochAcc.HeaderRecords[i])
+		newEpochAcc.currentEpoch.records = append(newEpochAcc.currentEpoch.records, tmp)
+	}
+
+	startDifficulty := bytesToUint256(epochAcc.HeaderRecords[epochRecordIndex][32:])
+
+	newEpochAcc.currentEpoch.difficulty = startDifficulty
+
+	for i := startNumber + 1; i <= 1000010; i++ {
+		header, err := getHeader(uint64(i))
+		assert.NoError(t, err)
+		err = newEpochAcc.Update(*header)
+		assert.NoError(t, err)
+		currIndex := GetHeaderRecordIndex(uint64(i))
+		assert.True(t, bytes.Equal(newEpochAcc.currentEpoch.records[currIndex], epochAcc.HeaderRecords[currIndex]))
+	}
+}
+
 // all test blocks are in the same epoch
 func parseHeaderWithProof() ([]BlockHeaderWithProof, error) {
 	headWithProofBytes, err := os.ReadFile("./testdata/header_with_proofs.json")
@@ -112,3 +144,8 @@ func getHeader(number uint64) (*types.Header, error) {
 	err = rlp.Decode(reader, head)
 	return head, err
 }
+
+func bytesToUint256(input []byte) *uint256.Int {
+	res := utils.ReverseBytes(input)
+	return uint256.MustFromBig(big.NewInt(0).SetBytes(res))
+}
diff --git a/portalnetwork/storage/content_storage.go b/portalnetwork/storage/content_storage.go
index 8b9b9a389bb4..9f24fb08dfb9 100644
--- a/portalnetwork/storage/content_storage.go
+++ b/portalnetwork/storage/content_storage.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/portalnetwork/utils"
 	"github.com/holiman/uint256"
 	sqlite3 "github.com/mattn/go-sqlite3"
 )
@@ -285,7 +286,7 @@ func (p *ContentStorage) GetLargestDistance() (*uint256.Int, error) {
 		return nil, err
 	}
 	// reverse the distance, because big.SetBytes is big-endian
-	reverseBytes(distance)
+	utils.ReverseBytesInPlace(distance)
 	bigNum := new(big.Int).SetBytes(distance)
 	res := uint256.MustFromBig(bigNum)
 	return res, nil
@@ -385,9 +386,3 @@ func (p *ContentStorage) deleteContentOutOfRadius(radius *uint256.Int) error {
 func (p *ContentStorage) ForcePrune(radius *uint256.Int) error {
 	return p.deleteContentOutOfRadius(radius)
 }
-
-func reverseBytes(src []byte) {
-	for i := 0; i < len(src)/2; i++ {
-		src[i], src[len(src)-i-1] = src[len(src)-i-1], src[i]
-	}
-}
diff --git a/portalnetwork/utils/bytes.go b/portalnetwork/utils/bytes.go
new file mode 100644
index 000000000000..0205d31ca725
--- /dev/null
+++ b/portalnetwork/utils/bytes.go
@@ -0,0 +1,16 @@
+package utils
+
+func ReverseBytesInPlace(src []byte) {
+	for i := 0; i < len(src)/2; i++ {
+		src[i], src[len(src)-i-1] = src[len(src)-i-1], src[i]
+	}
+}
+
+func ReverseBytes(src []byte) []byte {
+	lenth := len(src)
+	dst := make([]byte, lenth)
+	for i := 0; i < len(src); i++ {
+		dst[lenth-1-i] = src[i]
+	}
+	return dst
+}