diff --git a/pkg/keyspace/keyspace.go b/pkg/keyspace/keyspace.go
index 6fa4941b1784..adcb0be3106c 100644
--- a/pkg/keyspace/keyspace.go
+++ b/pkg/keyspace/keyspace.go
@@ -515,9 +515,9 @@ func (manager *Manager) UpdateKeyspaceState(name string, newState keyspacepb.Key
 	// Changing the state of default keyspace is not allowed.
 	if name == utils.DefaultKeyspaceName {
 		log.Warn("[keyspace] failed to update keyspace config",
-			zap.Error(errModifyDefault),
+			zap.Error(ErrModifyDefaultKeyspace),
 		)
-		return nil, errModifyDefault
+		return nil, ErrModifyDefaultKeyspace
 	}
 	var meta *keyspacepb.KeyspaceMeta
 	err := manager.store.RunInTxn(manager.ctx, func(txn kv.Txn) error {
@@ -567,9 +567,9 @@ func (manager *Manager) UpdateKeyspaceStateByID(id uint32, newState keyspacepb.K
 	// Changing the state of default keyspace is not allowed.
 	if id == utils.DefaultKeyspaceID {
 		log.Warn("[keyspace] failed to update keyspace config",
-			zap.Error(errModifyDefault),
+			zap.Error(ErrModifyDefaultKeyspace),
 		)
-		return nil, errModifyDefault
+		return nil, ErrModifyDefaultKeyspace
 	}
 	var meta *keyspacepb.KeyspaceMeta
 	var err error
diff --git a/pkg/keyspace/tso_keyspace_group.go b/pkg/keyspace/tso_keyspace_group.go
index a1cc9a0e9b0f..ce9af8600398 100644
--- a/pkg/keyspace/tso_keyspace_group.go
+++ b/pkg/keyspace/tso_keyspace_group.go
@@ -536,6 +536,16 @@ func (m *GroupManager) SplitKeyspaceGroupByID(
 		if splitSourceKg.IsMerging() {
 			return ErrKeyspaceGroupInMerging(splitSourceID)
 		}
+		// Build the new keyspace groups for split source and target.
+		var startKeyspaceID, endKeyspaceID uint32
+		if len(keyspaceIDRange) >= 2 {
+			startKeyspaceID, endKeyspaceID = keyspaceIDRange[0], keyspaceIDRange[1]
+		}
+		splitSourceKeyspaces, splitTargetKeyspaces, err := buildSplitKeyspaces(
+			splitSourceKg.Keyspaces, keyspaces, startKeyspaceID, endKeyspaceID)
+		if err != nil {
+			return err
+		}
 		// Check if the source keyspace group has enough replicas.
 		if len(splitSourceKg.Members) < utils.DefaultKeyspaceGroupReplicaCount {
 			return ErrKeyspaceGroupNotEnoughReplicas
@@ -548,15 +558,6 @@ func (m *GroupManager) SplitKeyspaceGroupByID(
 		if splitTargetKg != nil {
 			return ErrKeyspaceGroupExists
 		}
-		var startKeyspaceID, endKeyspaceID uint32
-		if len(keyspaceIDRange) >= 2 {
-			startKeyspaceID, endKeyspaceID = keyspaceIDRange[0], keyspaceIDRange[1]
-		}
-		splitSourceKeyspaces, splitTargetKeyspaces, err := buildSplitKeyspaces(
-			splitSourceKg.Keyspaces, keyspaces, startKeyspaceID, endKeyspaceID)
-		if err != nil {
-			return err
-		}
 		// Update the old keyspace group.
 		splitSourceKg.Keyspaces = splitSourceKeyspaces
 		splitSourceKg.SplitState = &endpoint.SplitState{
@@ -606,6 +607,9 @@ func buildSplitKeyspaces(
 			oldKeyspaceMap[keyspace] = struct{}{}
 		}
 		for _, keyspace := range new {
+			if keyspace == utils.DefaultKeyspaceID {
+				return nil, nil, ErrModifyDefaultKeyspace
+			}
 			if _, ok := oldKeyspaceMap[keyspace]; !ok {
 				return nil, nil, ErrKeyspaceNotInKeyspaceGroup
 			}
@@ -618,15 +622,7 @@ func buildSplitKeyspaces(
 				oldSplit = append(oldSplit, keyspace)
 			}
 		}
-		// Dedup new keyspaces if it's necessary.
-		if newNum == len(newKeyspaceMap) {
-			return oldSplit, new, nil
-		}
-		newSplit := make([]uint32, 0, len(newKeyspaceMap))
-		for keyspace := range newKeyspaceMap {
-			newSplit = append(newSplit, keyspace)
-		}
-		return oldSplit, newSplit, nil
+		return oldSplit, new, nil
 	}
 	// Split according to the start and end keyspace ID.
 	if startKeyspaceID == 0 && endKeyspaceID == 0 {
@@ -637,6 +633,9 @@ func buildSplitKeyspaces(
 		newKeyspaceMap = make(map[uint32]struct{}, newNum)
 	)
 	for _, keyspace := range old {
+		if keyspace == utils.DefaultKeyspaceID {
+			return nil, nil, ErrModifyDefaultKeyspace
+		}
 		if startKeyspaceID <= keyspace && keyspace <= endKeyspaceID {
 			newSplit = append(newSplit, keyspace)
 			newKeyspaceMap[keyspace] = struct{}{}
@@ -770,7 +769,9 @@ func (m *GroupManager) AllocNodesForKeyspaceGroup(id uint32, desiredReplicaCount
 		return nil, err
 	}
 	m.groups[endpoint.StringUserKind(kg.UserKind)].Put(kg)
-	log.Info("alloc nodes for keyspace group", zap.Uint32("keyspace-group-id", id), zap.Reflect("nodes", nodes))
+	log.Info("alloc nodes for keyspace group",
+		zap.Uint32("keyspace-group-id", id),
+		zap.Reflect("nodes", nodes))
 	return nodes, nil
 }
 
@@ -906,20 +907,17 @@ func (m *GroupManager) MergeKeyspaceGroups(mergeTargetID uint32, mergeList []uin
 			}
 			groups[kgID] = kg
 		}
+		// Build the new keyspaces for the merge target keyspace group.
 		mergeTargetKg = groups[mergeTargetID]
 		keyspaces := make(map[uint32]struct{})
 		for _, keyspace := range mergeTargetKg.Keyspaces {
 			keyspaces[keyspace] = struct{}{}
 		}
-		// Delete the keyspace groups in merge list and move the keyspaces in it to the target keyspace group.
 		for _, kgID := range mergeList {
 			kg := groups[kgID]
 			for _, keyspace := range kg.Keyspaces {
 				keyspaces[keyspace] = struct{}{}
 			}
-			if err := m.store.DeleteKeyspaceGroup(txn, kg.ID); err != nil {
-				return err
-			}
 		}
 		mergedKeyspaces := make([]uint32, 0, len(keyspaces))
 		for keyspace := range keyspaces {
@@ -933,7 +931,17 @@ func (m *GroupManager) MergeKeyspaceGroups(mergeTargetID uint32, mergeList []uin
 		mergeTargetKg.MergeState = &endpoint.MergeState{
 			MergeList: mergeList,
 		}
-		return m.store.SaveKeyspaceGroup(txn, mergeTargetKg)
+		err = m.store.SaveKeyspaceGroup(txn, mergeTargetKg)
+		if err != nil {
+			return err
+		}
+		// Delete the keyspace groups in merge list and move the keyspaces in it to the target keyspace group.
+		for _, kgID := range mergeList {
+			if err := m.store.DeleteKeyspaceGroup(txn, kgID); err != nil {
+				return err
+			}
+		}
+		return nil
 	}); err != nil {
 		return err
 	}
@@ -948,7 +956,10 @@ func (m *GroupManager) MergeKeyspaceGroups(mergeTargetID uint32, mergeList []uin
 
 // FinishMergeKeyspaceByID finishes the merging keyspace group by the merge target ID.
 func (m *GroupManager) FinishMergeKeyspaceByID(mergeTargetID uint32) error {
-	var mergeTargetKg *endpoint.KeyspaceGroup
+	var (
+		mergeTargetKg *endpoint.KeyspaceGroup
+		mergeList     []uint32
+	)
 	m.Lock()
 	defer m.Unlock()
 	if err := m.store.RunInTxn(m.ctx, func(txn kv.Txn) (err error) {
@@ -974,6 +985,7 @@ func (m *GroupManager) FinishMergeKeyspaceByID(mergeTargetID uint32) error {
 				return ErrKeyspaceGroupNotInMerging(kgID)
 			}
 		}
+		mergeList = mergeTargetKg.MergeState.MergeList
 		mergeTargetKg.MergeState = nil
 		return m.store.SaveKeyspaceGroup(txn, mergeTargetKg)
 	}); err != nil {
@@ -981,5 +993,8 @@ func (m *GroupManager) FinishMergeKeyspaceByID(mergeTargetID uint32) error {
 	}
 	// Update the keyspace group cache.
 	m.groups[endpoint.StringUserKind(mergeTargetKg.UserKind)].Put(mergeTargetKg)
+	log.Info("finish merge keyspace group",
+		zap.Uint32("merge-target-id", mergeTargetKg.ID),
+		zap.Reflect("merge-list", mergeList))
 	return nil
 }
diff --git a/pkg/keyspace/tso_keyspace_group_test.go b/pkg/keyspace/tso_keyspace_group_test.go
index 0eb71d2d5c4e..40b779382cd4 100644
--- a/pkg/keyspace/tso_keyspace_group_test.go
+++ b/pkg/keyspace/tso_keyspace_group_test.go
@@ -238,8 +238,9 @@ func (suite *keyspaceGroupTestSuite) TestKeyspaceGroupSplit() {
 
 	keyspaceGroups := []*endpoint.KeyspaceGroup{
 		{
-			ID:       uint32(1),
-			UserKind: endpoint.Basic.String(),
+			ID:        uint32(1),
+			UserKind:  endpoint.Basic.String(),
+			Keyspaces: []uint32{444},
 		},
 		{
 			ID:        uint32(2),
@@ -250,8 +251,11 @@ func (suite *keyspaceGroupTestSuite) TestKeyspaceGroupSplit() {
 	}
 	err := suite.kgm.CreateKeyspaceGroups(keyspaceGroups)
 	re.NoError(err)
+	// split the default keyspace
+	err = suite.kgm.SplitKeyspaceGroupByID(0, 4, []uint32{utils.DefaultKeyspaceID})
+	re.ErrorIs(err, ErrModifyDefaultKeyspace)
 	// split the keyspace group 1 to 4
-	err = suite.kgm.SplitKeyspaceGroupByID(1, 4, []uint32{333})
+	err = suite.kgm.SplitKeyspaceGroupByID(1, 4, []uint32{444})
 	re.ErrorIs(err, ErrKeyspaceGroupNotEnoughReplicas)
 	// split the keyspace group 2 to 4 without giving any keyspace
 	err = suite.kgm.SplitKeyspaceGroupByID(2, 4, []uint32{})
@@ -316,7 +320,7 @@ func (suite *keyspaceGroupTestSuite) TestKeyspaceGroupSplit() {
 	err = suite.kgm.SplitKeyspaceGroupByID(3, 5, nil)
 	re.ErrorContains(err, ErrKeyspaceGroupNotExists(3).Error())
 	// split into an existing keyspace group
-	err = suite.kgm.SplitKeyspaceGroupByID(2, 4, nil)
+	err = suite.kgm.SplitKeyspaceGroupByID(2, 4, []uint32{111})
 	re.ErrorIs(err, ErrKeyspaceGroupExists)
 	// split with the wrong keyspaces.
 	err = suite.kgm.SplitKeyspaceGroupByID(2, 5, []uint32{111, 222, 444})
diff --git a/pkg/keyspace/util.go b/pkg/keyspace/util.go
index ac8168aa5f21..bf4f8413bb17 100644
--- a/pkg/keyspace/util.go
+++ b/pkg/keyspace/util.go
@@ -80,8 +80,9 @@ var (
 	ErrNoAvailableNode = errors.New("no available node")
 	// ErrExceedMaxEtcdTxnOps is used to indicate the number of etcd txn operations exceeds the limit.
 	ErrExceedMaxEtcdTxnOps = errors.New("exceed max etcd txn operations")
-	errModifyDefault       = errors.New("cannot modify default keyspace's state")
-	errIllegalOperation    = errors.New("unknown operation")
+	// ErrModifyDefaultKeyspace is used to indicate that default keyspace cannot be modified.
+	ErrModifyDefaultKeyspace = errors.New("cannot modify default keyspace's state")
+	errIllegalOperation      = errors.New("unknown operation")
 
 	// stateTransitionTable lists all allowed next state for the given current state.
 	// Note that transit from any state to itself is allowed for idempotence.