diff --git a/docs/chapter_computational_complexity/time_complexity.md b/docs/chapter_computational_complexity/time_complexity.md
index 5a44a17f1..e567718a5 100644
--- a/docs/chapter_computational_complexity/time_complexity.md
+++ b/docs/chapter_computational_complexity/time_complexity.md
@@ -601,8 +601,8 @@ $$
             console.log(0);
         }
         // +n*n（技巧 3）
-        for (var i = 0; i < 2 * n; i++) {
-            for (var j = 0; j < n + 1; j++) {
+        for (let i = 0; i < 2 * n; i++) {
+            for (let j = 0; j < n + 1; j++) {
                 console.log(0);
             }
         }