diff --git a/source/libs/executor/inc/tfill.h b/source/libs/executor/inc/tfill.h
index 78b3cd2f40b839dddd39d12bf0b0d6fc1ba82555..79837480d79ad265e8e6ce307a09828a3dc5e1d7 100644
--- a/source/libs/executor/inc/tfill.h
+++ b/source/libs/executor/inc/tfill.h
@@ -120,6 +120,8 @@ int64_t getNumOfResultsAfterFillGap(SFillInfo* pFillInfo, int64_t ekey, int32_t
 void          taosFillSetStartInfo(struct SFillInfo* pFillInfo, int32_t numOfRows, TSKEY endKey);
 void          taosResetFillInfo(struct SFillInfo* pFillInfo, TSKEY startTimestamp);
 void          taosFillSetInputDataBlock(struct SFillInfo* pFillInfo, const struct SSDataBlock* pInput);
+void          taosFillUpdateStartTimestampInfo(SFillInfo* pFillInfo, int64_t ts);
+bool          taosFillNotStarted(const SFillInfo* pFillInfo);
 SFillColInfo* createFillColInfo(SExprInfo* pExpr, int32_t numOfFillExpr, SExprInfo* pNotFillExpr,
                                 int32_t numOfNotFillCols, const struct SNodeListNode* val);
 bool          taosFillHasMoreResults(struct SFillInfo* pFillInfo);
diff --git a/source/libs/executor/src/filloperator.c b/source/libs/executor/src/filloperator.c
index 839c845bac73817e916f30e2ffa61e9ad4a3b227..3d1df6482ec7d8c32557a90d049ab4a2f380c8b3 100644
--- a/source/libs/executor/src/filloperator.c
+++ b/source/libs/executor/src/filloperator.c
@@ -139,6 +139,12 @@ static SSDataBlock* doFillImpl(SOperatorInfo* pOperator) {
   }
 
   SOperatorInfo* pDownstream = pOperator->pDownstream[0];
+
+  // the scan order may be different from the output result order for agg interval operator.
+  if (pDownstream->operatorType == QUERY_NODE_PHYSICAL_PLAN_HASH_INTERVAL) {
+    order = ((SIntervalAggOperatorInfo*) pDownstream->info)->resultTsOrder;
+  }
+
   while (1) {
     SSDataBlock* pBlock = pDownstream->fpSet.getNextFn(pDownstream);
     if (pBlock == NULL) {
@@ -162,11 +168,24 @@ static SSDataBlock* doFillImpl(SOperatorInfo* pOperator) {
         pInfo->curGroupId = pInfo->pRes->info.id.groupId;  // the first data block
         pInfo->totalInputRows += pInfo->pRes->info.rows;
 
-        if (order == pInfo->pFillInfo->order) {
+        if (order == TSDB_ORDER_ASC) {
+          int64_t skey = pBlock->info.window.skey;
+          if (skey < pInfo->pFillInfo->start) {  // the start key may be smaller than the
+            ASSERT( taosFillNotStarted(pInfo->pFillInfo));
+            taosFillUpdateStartTimestampInfo(pInfo->pFillInfo, skey);
+          }
+
           taosFillSetStartInfo(pInfo->pFillInfo, pInfo->pRes->info.rows, pBlock->info.window.ekey);
         } else {
+          int64_t ekey = pBlock->info.window.ekey;
+          if (ekey > pInfo->pFillInfo->start) {
+            ASSERT( taosFillNotStarted(pInfo->pFillInfo));
+            taosFillUpdateStartTimestampInfo(pInfo->pFillInfo, ekey);
+          }
+
           taosFillSetStartInfo(pInfo->pFillInfo, pInfo->pRes->info.rows, pBlock->info.window.skey);
         }
+
         taosFillSetInputDataBlock(pInfo->pFillInfo, pInfo->pRes);
       } else if (pInfo->curGroupId != pBlock->info.id.groupId) {  // the new group data block
         pInfo->existNewGroupBlock = pBlock;
@@ -256,11 +275,8 @@ static int32_t initFillInfo(SFillOperatorInfo* pInfo, SExprInfo* pExpr, int32_t
                             const char* id, SInterval* pInterval, int32_t fillType, int32_t order) {
   SFillColInfo* pColInfo = createFillColInfo(pExpr, numOfCols, pNotFillExpr, numOfNotFillCols, pValNode);
 
-  STimeWindow w = {0};
-  int64_t     startKey = (order == TSDB_ORDER_ASC) ? win.skey : win.ekey;
-
-  getInitialStartTimeWindow(pInterval, startKey, &w, order == TSDB_ORDER_ASC);
-  pInfo->pFillInfo = taosCreateFillInfo(w.skey, numOfCols, numOfNotFillCols, capacity, pInterval, fillType, pColInfo,
+  int64_t startKey = (order == TSDB_ORDER_ASC) ? win.skey : win.ekey;
+  pInfo->pFillInfo = taosCreateFillInfo(startKey, numOfCols, numOfNotFillCols, capacity, pInterval, fillType, pColInfo,
                                         pInfo->primaryTsCol, order, id);
 
   if (order == TSDB_ORDER_ASC) {
diff --git a/source/libs/executor/src/tfill.c b/source/libs/executor/src/tfill.c
index e4d5d2c268bbc76e79b72384139dcd42f2b510e9..7cc50a70ab799184de5b350f72526ee44ac23295 100644
--- a/source/libs/executor/src/tfill.c
+++ b/source/libs/executor/src/tfill.c
@@ -517,11 +517,16 @@ void taosFillSetStartInfo(SFillInfo* pFillInfo, int32_t numOfRows, TSKEY endKey)
     return;
   }
 
+  // the endKey is now the aligned time window value. truncate time window isn't correct.
   pFillInfo->end = endKey;
-  if (!FILL_IS_ASC_FILL(pFillInfo)) {
-    pFillInfo->end = taosTimeTruncate(endKey, &pFillInfo->interval);
-    pFillInfo->end = taosTimeAdd(pFillInfo->end, pFillInfo->interval.interval, pFillInfo->interval.intervalUnit,pFillInfo->interval.precision);
+
+#if 0
+  if (pFillInfo->order == TSDB_ORDER_ASC) {
+    ASSERT(pFillInfo->start <= pFillInfo->end);
+  } else {
+    ASSERT(pFillInfo->start >= pFillInfo->end);
   }
+#endif
 
   pFillInfo->index = 0;
   pFillInfo->numOfRows = numOfRows;
@@ -531,6 +536,13 @@ void taosFillSetInputDataBlock(SFillInfo* pFillInfo, const SSDataBlock* pInput)
   pFillInfo->pSrcBlock = (SSDataBlock*)pInput;
 }
 
+void taosFillUpdateStartTimestampInfo(SFillInfo* pFillInfo, int64_t ts) {
+  pFillInfo->start = ts;
+  pFillInfo->currentKey = ts;
+}
+
+bool taosFillNotStarted(const SFillInfo* pFillInfo) {return pFillInfo->start == pFillInfo->currentKey;}
+
 bool taosFillHasMoreResults(SFillInfo* pFillInfo) {
   int32_t remain = taosNumOfRemainRows(pFillInfo);
   if (remain > 0) {
@@ -565,6 +577,7 @@ int64_t getNumOfResultsAfterFillGap(SFillInfo* pFillInfo, TSKEY ekey, int32_t ma
         (ekey1 > pFillInfo->currentKey && !FILL_IS_ASC_FILL(pFillInfo))) {
       return 0;
     }
+
     numOfRes = taosTimeCountInterval(ekey1, pFillInfo->currentKey, pFillInfo->interval.sliding,
                                      pFillInfo->interval.slidingUnit, pFillInfo->interval.precision);
     numOfRes += 1;
diff --git a/tests/script/tsim/query/partitionby.sim b/tests/script/tsim/query/partitionby.sim
index da7dfc00908c7a20c3a8831c724187dc92746313..76d4f87908590839cdec1e8689404be974d4e86d 100644
--- a/tests/script/tsim/query/partitionby.sim
+++ b/tests/script/tsim/query/partitionby.sim
@@ -121,7 +121,7 @@ sql select count(*) from (select ts from $mt1 where ts is not null partition by
 if $rows != 1 then
   return -1
 endi
-if $data00 != 2 then
+if $data00 != 4 then
   return -1
 endi
 
@@ -129,7 +129,7 @@ sql select count(*) from (select ts from $mt1 where ts is not null partition by
 if $rows != 1 then
   return -1
 endi
-if $data00 != 8 then
+if $data00 != 16 then
   return -1
 endi