diff --git a/packages/theme-chalk/src/menu.scss b/packages/theme-chalk/src/menu.scss
index 1a0b4a8e53534..5083c0f24e3ed 100644
--- a/packages/theme-chalk/src/menu.scss
+++ b/packages/theme-chalk/src/menu.scss
@@ -53,6 +53,7 @@
   margin: 0;
   padding-left: 0;
   background-color: var(--el-menu-background-color);
+  box-sizing: border-box;
   @include utils-clearfix;
   &.#{$namespace}-menu--horizontal {
     border-bottom: solid 1px var(--el-menu-border-color);