diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index a20ecd344d..f2cd9313e1 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -1690,17 +1690,20 @@ int32_t blockDataTrimFirstRows(SSDataBlock* pBlock, size_t n) {
 static void colDataKeepFirstNRows(SColumnInfoData* pColInfoData, size_t n, size_t total) {
   if (n >= total || n == 0) return;
   if (IS_VAR_DATA_TYPE(pColInfoData->info.type)) {
-    int32_t newLen = -1;
-    for (int i = n; i >= 0; --i) {
-      if (pColInfoData->varmeta.offset[i] != -1) {
+    int32_t newLen = pColInfoData->varmeta.offset[n];
+    if (-1 == newLen) {
+      for (int i = n - 1; i >= 0; --i) {
         newLen = pColInfoData->varmeta.offset[i];
-        break;
+        if (newLen != -1) {
+          if (pColInfoData->info.type == TSDB_DATA_TYPE_JSON) {
+            newLen += getJsonValueLen(pColInfoData->pData + newLen);
+          } else {
+            newLen += varDataTLen(pColInfoData->pData + newLen);
+          }
+          break;
+        }
       }
     }
-    if(-1 == newLen) {
-      return;
-    }
-
     pColInfoData->varmeta.length = newLen;
     // pColInfoData->varmeta.length = colDataMoveVarData(pColInfoData, 0, n);
     memset(&pColInfoData->varmeta.offset[n], 0, total - n);