diff --git a/inventory-web/src/views/stock/stocktake/index.vue b/inventory-web/src/views/stock/stocktake/index.vue
index 3b98987..dddd2dc 100644
--- a/inventory-web/src/views/stock/stocktake/index.vue
+++ b/inventory-web/src/views/stock/stocktake/index.vue
@@ -1651,6 +1651,18 @@ const handleListLimitChange = (limit: number) => {
 
 // ★ 新增: 更新实盘数量（手动修改）
 const handleQuantityChange = async (row: any, val: number) => {
+  row.quantity = val
+
+  // ★ 本地实时联动「差异」列。
+  //   盲盘保护：后端在 blind 模式下把 stock_qty 置为 null（绝不下发账面数），
+  //   此时**不做任何减法**，保持 diff_qty 原状（null → 渲染为「—」），
+  //   否则用 null 参与运算会算出错误的差异，等于绕过了盲盘限制。
+  if (row.stock_qty !== null && row.stock_qty !== undefined) {
+    // 与后端一致保留 4 位小数，避免浮点尾差显示成 4.999999999
+    const diff = Number(val || 0) - Number(row.stock_qty || 0)
+    row.diff_qty = Math.round(diff * 10000) / 10000
+  }
+
   try {
     await updateStocktakeQuantity({
       stock_id: row.stock_id,