diff --git a/src/sql/engine/join/ob_merge_join_op.cpp b/src/sql/engine/join/ob_merge_join_op.cpp
index aaf05a20a6..a59ff0ec28 100644
--- a/src/sql/engine/join/ob_merge_join_op.cpp
+++ b/src/sql/engine/join/ob_merge_join_op.cpp
@@ -963,28 +963,22 @@ int ObMergeJoinOp::ChildBatchFetcher::init(
 int ObMergeJoinOp::ChildBatchFetcher::get_next_batch(const int64_t max_row_cnt)
 {
   int ret = OB_SUCCESS;
-  if (OB_UNLIKELY(0 != backup_rows_cnt_)) {
+  const int64_t remain_backup_rows = backup_rows_cnt_ - backup_rows_used_;
+  if (OB_UNLIKELY(0 != remain_backup_rows)) {
     if (OB_UNLIKELY(backup_datums_.count() != all_exprs_->count())) {
       ret = OB_ERR_UNEXPECTED;
       LOG_WARN("store datums cnt and child output cnt not equal", K(ret),
                 K(backup_datums_.count()), K(all_exprs_->count()));
     } else {
-      const int64_t restore_cnt = MIN(max_row_cnt, backup_rows_cnt_);
+      const int64_t restore_cnt = MIN(max_row_cnt, remain_backup_rows);
       for (int64_t i = 0; i < backup_datums_.count(); i++) {
         ObDatum *datum = all_exprs_->at(i)->locate_batch_datums(merge_join_op_.eval_ctx_);
-        MEMCPY(datum, backup_datums_.at(i), sizeof(ObDatum) * restore_cnt);
+        MEMCPY(datum, backup_datums_.at(i) + backup_rows_used_, sizeof(ObDatum) * restore_cnt);
       }
       brs_.size_ = restore_cnt;
       brs_.end_ = false;
       brs_.skip_ = NULL;
-      backup_rows_cnt_ -= restore_cnt;
-      if (OB_LIKELY(0 == backup_rows_cnt_)) {
-        backup_datums_.reset();
-      } else {
-        for (int64_t i = 0; i < backup_datums_.count(); i++) {
-          backup_datums_.at(i) = backup_datums_.at(i) + restore_cnt;
-        }
-      }
+      backup_rows_used_ += restore_cnt;
     }
   } else {
     if (brs_.end_) {
@@ -1021,21 +1015,36 @@ int ObMergeJoinOp::ChildBatchFetcher::backup_remain_rows()
   if (OB_UNLIKELY(cur_idx_ >= brs_.size_)) {
     ret = OB_ERR_UNEXPECTED;
     LOG_WARN("no remain rows", K(ret), K(cur_idx_), K(brs_.size_));
-  } else {
-    int64_t alloc_size = sizeof(ObDatum) * (brs_.size_ - cur_idx_);
+  } else if (backup_datums_.empty()) {
+    int64_t alloc_size = sizeof(ObDatum) * merge_join_op_.spec_.max_batch_size_;
     for (int64_t i = 0; i < all_exprs_->count() && OB_SUCC(ret); i++) {
-      backup_rows_cnt_ = 0;
       ObDatum *datum = NULL;
-      ObDatumVector src_datum = all_exprs_->at(i)->locate_expr_datumvector(merge_join_op_.eval_ctx_);
       if (OB_ISNULL(datum = static_cast<ObDatum *>(allocator.alloc(alloc_size)))) {
         ret = OB_ALLOCATE_MEMORY_FAILED;
         LOG_WARN("allocate memory failed", K(ret));
       } else if (OB_FAIL(backup_datums_.push_back(datum))) {
         LOG_WARN("push back failed", K(ret));
-      } else {
-        for (int64_t j = cur_idx_; j < brs_.size_ && OB_SUCC(ret); j++) {
-          if (!brs_.skip_->contain(j)) {
-            datum[backup_rows_cnt_++] = *src_datum.at(j);
+      }
+    }
+  }
+  if (OB_SUCC(ret)) {
+    if (OB_UNLIKELY(all_exprs_->count() != backup_datums_.count())) {
+      ret = OB_ERR_UNEXPECTED;
+      LOG_WARN("count mismatch", K(ret), K(all_exprs_->count()), K(backup_datums_.count()));
+    } else {
+      for (int64_t i = 0; i < all_exprs_->count() && OB_SUCC(ret); i++) {
+        backup_rows_cnt_ = 0;
+        backup_rows_used_ = 0;
+        ObDatumVector src_datum = all_exprs_->at(i)->locate_expr_datumvector(merge_join_op_.eval_ctx_);
+        ObDatum *datum = backup_datums_.at(i);
+        if (OB_ISNULL(datum)) {
+          ret = OB_ERR_UNEXPECTED;
+          LOG_WARN("backup datums memory is null", K(ret), K(i), K(all_exprs_->count()));
+        } else {
+          for (int64_t j = cur_idx_; j < brs_.size_ && OB_SUCC(ret); j++) {
+            if (!brs_.skip_->contain(j)) {
+              datum[backup_rows_cnt_++] = *src_datum.at(j);
+            }
           }
         }
       }
diff --git a/src/sql/engine/join/ob_merge_join_op.h b/src/sql/engine/join/ob_merge_join_op.h
index e8fa59216f..6c83399dd4 100644
--- a/src/sql/engine/join/ob_merge_join_op.h
+++ b/src/sql/engine/join/ob_merge_join_op.h
@@ -214,7 +214,7 @@ private:
         cur_idx_(0), brs_(), batch_size_(0), child_(NULL),
         match_groups_(match_groups), merge_join_op_(merge_join_op),
         all_exprs_(NULL), datum_store_(), backup_datums_(),
-        backup_rows_cnt_(0), brs_holder_(),
+        backup_rows_cnt_(0), backup_rows_used_(0), brs_holder_(),
         equal_param_idx_(allocator)
     {}
     int init(const uint64_t tenant_id, bool is_left, ObOperator *child,
@@ -242,6 +242,7 @@ private:
       datum_store_.reuse();
       backup_datums_.reuse();
       backup_rows_cnt_ = 0;
+      backup_rows_used_ = 0;
       brs_holder_.reset();
     }
     // for destroy
@@ -254,6 +255,7 @@ private:
       datum_store_.reset();
       backup_datums_.reset();
       backup_rows_cnt_ = 0;
+      backup_rows_used_ = 0;
       brs_holder_.reset();
     }
     int64_t cur_idx_;
@@ -269,6 +271,7 @@ private:
     // We need store these rows and output first, then get batch from child and output directly.
     ObSEArray<ObDatum *, 256> backup_datums_;
     int64_t backup_rows_cnt_;
+    int64_t backup_rows_used_;
     ObBatchResultHolder brs_holder_;
 
     common::ObFixedArray<int64_t, common::ObIAllocator> equal_param_idx_;