diff --git a/backend/JiShop/src/main/java/com/jishop/cart/domain/Cart.java b/backend/JiShop/src/main/java/com/jishop/cart/domain/Cart.java
index 72a926b7..c310ae12 100644
--- a/backend/JiShop/src/main/java/com/jishop/cart/domain/Cart.java
+++ b/backend/JiShop/src/main/java/com/jishop/cart/domain/Cart.java
@@ -33,6 +33,6 @@ public Cart(User user, SaleProduct saleProduct, int quantity) {
     }
 
     public void updateQuantity(int quantity) {
-        this.quantity += quantity;
+        this.quantity = quantity;
     }
 }