diff --git a/src/storage/blocksstable/encoding/ob_micro_block_encoder.cpp b/src/storage/blocksstable/encoding/ob_micro_block_encoder.cpp
index 6660898132..a4afca3836 100644
--- a/src/storage/blocksstable/encoding/ob_micro_block_encoder.cpp
+++ b/src/storage/blocksstable/encoding/ob_micro_block_encoder.cpp
@@ -576,7 +576,7 @@ int ObMicroBlockEncoder::build_block(char *&buf, int64_t &size)
       if (OB_FAIL(set_row_data_pos(fix_data_size))) {
         LOG_WARN("set row data position failed", K(ret));
       } else {
-        header_->var_column_count_ = static_cast<int16_t>(var_data_encoders_.count());
+        header_->var_column_count_ = static_cast<uint16_t>(var_data_encoders_.count());
       }
     }
 
@@ -613,7 +613,7 @@ int ObMicroBlockEncoder::build_block(char *&buf, int64_t &size)
 
     // <5> fill header
     if (OB_SUCC(ret)) {
-      header_->row_count_ = static_cast<int16_t>(datum_rows_.count());
+      header_->row_count_ = static_cast<uint32_t>(datum_rows_.count());
       header_->encoding_has_out_row_column_ = has_out_row_column_;
 
       const int64_t header_size = header_->header_size_;
diff --git a/src/storage/blocksstable/encoding/ob_micro_block_encoder.h b/src/storage/blocksstable/encoding/ob_micro_block_encoder.h
index 2ee28e1ec2..f34712b116 100644
--- a/src/storage/blocksstable/encoding/ob_micro_block_encoder.h
+++ b/src/storage/blocksstable/encoding/ob_micro_block_encoder.h
@@ -38,7 +38,8 @@ public:
   static const int64_t DEFAULT_ESTIMATE_REAL_SIZE_PCT = 150;
 
   // maximum row count is restricted to 4 bytes in MicroBlockHeader
-  static const int64_t MAX_MICRO_BLOCK_ROW_CNT = UINT32_MAX;
+  // But all_col_datums_ is restricted to 64K, so we limit maximum row count to uint16_max
+  static const int64_t MAX_MICRO_BLOCK_ROW_CNT = UINT16_MAX;
   // Unlike ObMicroBlockWriter, ObMicroBlockEncoder internally uses ObRowWriter and ObIColumnEncoder
   // to form row and column data. Both ObRowWriter and ObIColumnEncoder check buffer capacity by
   // calling ObBufferWriter::advance_zero. If buffer size is not enough, they return failure.