diff --git a/cdc/scheduler/internal/v3/keyspan/splitter_write.go b/cdc/scheduler/internal/v3/keyspan/splitter_write.go
index 9773597b582..653328ba618 100644
--- a/cdc/scheduler/internal/v3/keyspan/splitter_write.go
+++ b/cdc/scheduler/internal/v3/keyspan/splitter_write.go
@@ -170,11 +170,11 @@ func (m *writeSplitter) splitRegionsByWrittenKeysV1(
 		restRegions := len(regions) - i
 		regionCount++
 		spanWriteWeight += regions[i].WrittenKeys
-		// If the restSpans count is one, and the restWeight is less than writeLimitPerSpan,
+		// If the restSpans count is one, and the restWeight is less than equal to writeLimitPerSpan,
 		// we will use the rest regions as the last span. If the restWeight is larger than writeLimitPerSpan,
-		// then we need to add more restSpans (restWeight / writeLimitPerSpan) to split the rest regions.
+		// then we need to add more restSpans (restWeight / writeLimitPerSpan) + 1 to split the rest regions.
 		if restSpans == 1 {
-			if restWeight < int64(writeLimitPerSpan) {
+			if restWeight <= int64(writeLimitPerSpan) {
 				spans = append(spans, tablepb.Span{
 					TableID:  tableID,
 					StartKey: tablepb.Key(decodeKey(regions[spanStartIndex].StartKey)),
@@ -191,11 +191,12 @@ func (m *writeSplitter) splitRegionsByWrittenKeysV1(
 				regionCounts = append(regionCounts, lastSpanRegionCount)
 				weights = append(weights, lastSpanWriteWeight)
 				writeKeys = append(writeKeys, lastSpanWriteKey)
+				spanStartIndex = len(regions)
 				break
 			}
 			// If the restWeight is larger than writeLimitPerSpan,
 			// then we need to update the restSpans.
-			restSpans = int(restWeight) / int(writeLimitPerSpan)
+			restSpans = int(restWeight)/int(writeLimitPerSpan) + 1
 		}
 
 		// If the restRegions is less than equal to restSpans,
@@ -237,6 +238,32 @@ func (m *writeSplitter) splitRegionsByWrittenKeysV1(
 			spanStartIndex = i + 1
 		}
 	}
+	// All regions should be processed and append to spans
+	if spanStartIndex != len(regions) {
+		spans = append(spans, tablepb.Span{
+			TableID:  tableID,
+			StartKey: tablepb.Key(decodeKey(regions[spanStartIndex].StartKey)),
+			EndKey:   tablepb.Key(decodeKey(regions[len(regions)-1].EndKey)),
+		})
+		lastSpanRegionCount := len(regions) - spanStartIndex
+		lastSpanWriteWeight := uint64(0)
+		lastSpanWriteKey := uint64(0)
+		for j := spanStartIndex; j < len(regions); j++ {
+			lastSpanWriteKey += regions[j].WrittenKeys
+			lastSpanWriteWeight += regions[j].WrittenKeys
+		}
+		regionCounts = append(regionCounts, lastSpanRegionCount)
+		weights = append(weights, lastSpanWriteWeight)
+		writeKeys = append(writeKeys, lastSpanWriteKey)
+		log.Warn("some regions are added to the last span, it should not appear",
+			zap.Int("spanStartIndex", spanStartIndex),
+			zap.Int("regionsLength", len(regions)),
+			zap.Int("restSpans", restSpans),
+			zap.Int64("restWeight", restWeight),
+			zap.Any("prevSpan", spans[len(spans)-2]),
+			zap.Any("lastSpan", spans[len(spans)-1]),
+		)
+	}
 	return &splitRegionsInfo{
 		RegionCounts: regionCounts,
 		Weights:      weights,
diff --git a/cdc/scheduler/internal/v3/keyspan/splitter_write_test.go b/cdc/scheduler/internal/v3/keyspan/splitter_write_test.go
index 2987857c776..6c69b7f20b1 100644
--- a/cdc/scheduler/internal/v3/keyspan/splitter_write_test.go
+++ b/cdc/scheduler/internal/v3/keyspan/splitter_write_test.go
@@ -227,13 +227,44 @@ func TestSplitRegionEven(t *testing.T) {
 	info := splitter.splitRegionsByWrittenKeysV1(tblID, regions, 5)
 	require.Len(t, info.RegionCounts, 5)
 	require.Len(t, info.Weights, 5)
+	count := 0
 	for i, w := range info.Weights {
 		if i == 4 {
 			require.Equal(t, uint64(9576), w, i)
 		} else {
 			require.Equal(t, uint64(9591), w, i)
 		}
+		count += info.RegionCounts[i]
 	}
+	require.Equal(t, count, regionCount)
+}
+
+func TestSplitLargeRegion(t *testing.T) {
+	tblID := model.TableID(1)
+	regionCount := spanRegionLimit*5 + 1000
+	regions := make([]pdutil.RegionInfo, regionCount)
+	for i := 0; i < regionCount; i++ {
+		regions[i] = pdutil.RegionInfo{
+			ID:          uint64(i),
+			StartKey:    "" + strconv.Itoa(i),
+			EndKey:      "" + strconv.Itoa(i),
+			WrittenKeys: 2,
+		}
+	}
+	splitter := newWriteSplitter(model.ChangeFeedID4Test("test", "test"), nil, 4)
+	info := splitter.splitRegionsByWrittenKeysV1(tblID, regions, 5)
+	require.Len(t, info.RegionCounts, 6)
+	require.Len(t, info.Weights, 6)
+	count := 0
+	for i, c := range info.RegionCounts {
+		if i == 5 {
+			require.Equal(t, 1000, c, i)
+		} else {
+			require.Equal(t, spanRegionLimit, c, i)
+		}
+		count += c
+	}
+	require.Equal(t, count, regionCount)
 }
 
 func TestSpanRegionLimitBase(t *testing.T) {
@@ -247,9 +278,12 @@ func TestSpanRegionLimitBase(t *testing.T) {
 	spanNum := getSpansNumber(len(regions), captureNum)
 	info := splitter.splitRegionsByWrittenKeysV1(0, cloneRegions(regions), spanNum)
 	require.Len(t, info.RegionCounts, spanNum)
+	count := 0
 	for _, c := range info.RegionCounts {
 		require.LessOrEqual(t, c, int(spanRegionLimit*1.1))
+		count += c
 	}
+	require.Equal(t, count, len(regions))
 }
 
 func TestSpanRegionLimit(t *testing.T) {
@@ -273,7 +307,7 @@ func TestSpanRegionLimit(t *testing.T) {
 	}
 
 	// total region number
-	totalRegionNumbers := spanRegionLimit * 10
+	totalRegionNumbers := spanRegionLimit*10 + 100
 
 	// writtenKeys over 20000 percentage
 	percentOver20000 := 1
@@ -318,7 +352,12 @@ func TestSpanRegionLimit(t *testing.T) {
 	spanNum := getSpansNumber(len(regions), captureNum)
 	info := splitter.splitRegionsByWrittenKeysV1(0, cloneRegions(regions), spanNum)
 	require.LessOrEqual(t, spanNum, len(info.RegionCounts))
-	for _, c := range info.RegionCounts {
-		require.LessOrEqual(t, c, int(spanRegionLimit*1.1))
+	count := 0
+	for i, c := range info.RegionCounts {
+		if i != len(info.RegionCounts)-1 {
+			require.LessOrEqual(t, c, int(spanRegionLimit*1.1))
+		}
+		count += c
 	}
+	require.Equal(t, count, totalRegionNumbers)
 }