diff --git a/deps/common/lang/cmath.h b/deps/common/lang/cmath.h
new file mode 100644
index 000000000..f25cfcef2
--- /dev/null
+++ b/deps/common/lang/cmath.h
@@ -0,0 +1,14 @@
+/* Copyright (c) 2021 OceanBase and/or its affiliates. All rights reserved.
+miniob is licensed under Mulan PSL v2.
+You can use this software according to the terms and conditions of the Mulan PSL v2.
+You may obtain a copy of Mulan PSL v2 at:
+         http://license.coscl.org.cn/MulanPSL2
+THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+See the Mulan PSL v2 for more details. */
+#pragma once
+
+#include <cmath>
+
+using std::round;
\ No newline at end of file
diff --git a/deps/common/lang/string.cpp b/deps/common/lang/string.cpp
index de8c7af1e..11a8d3593 100644
--- a/deps/common/lang/string.cpp
+++ b/deps/common/lang/string.cpp
@@ -22,6 +22,7 @@ See the Mulan PSL v2 for more details. */
 
 #include "common/log/log.h"
 #include "common/lang/algorithm.h"
+#include "common/lang/cmath.h"
 #include "common/lang/iomanip.h"
 
 namespace common {
@@ -270,7 +271,8 @@ char *substr(const char *s, int n1, int n2)
 string double_to_str(double v)
 {
   char buf[256];
-  snprintf(buf, sizeof(buf), "%.2f", v);
+  double rounded_v = round(v * 100.0) / 100.0;
+  snprintf(buf, sizeof(buf), "%.2f", rounded_v);
   size_t len = strlen(buf);
   while (buf[len - 1] == '0') {
     len--;
diff --git a/docs/docs/game/miniob-output-convention.md b/docs/docs/game/miniob-output-convention.md
index 15999d0c8..96d165fcf 100644
--- a/docs/docs/game/miniob-output-convention.md
+++ b/docs/docs/game/miniob-output-convention.md
@@ -28,7 +28,7 @@ NOTE：后台测试程序，是将预先编辑好的Case执行后，将执行结
 4. 所有输出不区分大小写
 5. 日期(date)输出格式使用："YYYY-mm-DD"
 6. 输出的字符串不使用单引号双引号或其它括起来
-7. 浮点数输出，不要带后面多余的0，可以参考C sprintf的%g格式输出，保留两位小数。参考函数 double_to_str
+7. 浮点数输出，不要带后面多余的0，四舍五入保留两位小数。参考函数 double_to_str
 
 FAQ
 - 某张表或者某个查询结果一行数据都没有，但是依然需要输出表头信息