diff --git a/library/think/db/Builder.php b/library/think/db/Builder.php
index 41700d9f..d5c7e9ab 100644
--- a/library/think/db/Builder.php
+++ b/library/think/db/Builder.php
@@ -302,7 +302,7 @@ abstract class Builder
 
         // 查询规则和条件
         if (!is_array($val)) {
-            $val = ['=', $val];
+            $val = is_null($val) ? ['null', ''] : ['=', $val];
         }
         list($exp, $value) = $val;