diff --git a/backend/src/main/java/com/linhelp/delivery/DeliveryAssignmentService.java b/backend/src/main/java/com/linhelp/delivery/DeliveryAssignmentService.java
index 903d551..b7e7488 100644
--- a/backend/src/main/java/com/linhelp/delivery/DeliveryAssignmentService.java
+++ b/backend/src/main/java/com/linhelp/delivery/DeliveryAssignmentService.java
@@ -62,6 +62,7 @@ public class DeliveryAssignmentService {
         task.setBizType(BIZ_TYPE_GOODS_ORDER);
         task.setBizOrderId(order.getId());
         task.setBizOrderNo(order.getOrderNo());
+        ensureNotAssigned(task.getBizType(), task.getBizOrderId());
         enrichAddressContact(task, order.getUserId(), order.getAddressId());
         task.setAmountCent(order.getPayableAmountCent());
         task.setRemark(order.getRemark());
@@ -82,6 +83,7 @@ public class DeliveryAssignmentService {
         task.setBizType(BIZ_TYPE_EXPRESS_ORDER);
         task.setBizOrderId(order.getId());
         task.setBizOrderNo(order.getOrderNo());
+        ensureNotAssigned(task.getBizType(), task.getBizOrderId());
         task.setContactName(order.getContactName());
         task.setContactPhone(order.getContactPhone());
         task.setAddress(order.getDeliveryAddress());
@@ -107,6 +109,7 @@ public class DeliveryAssignmentService {
         task.setBizType(BIZ_TYPE_GROUP_BUY_ORDER);
         task.setBizOrderId(order.getId());
         task.setBizOrderNo(order.getOrderNo());
+        ensureNotAssigned(task.getBizType(), task.getBizOrderId());
         enrichAddressContact(task, order.getUserId(), order.getAddressId());
         task.setAmountCent(order.getAmountCent());
         task.setRemark(order.getRemark());
@@ -171,6 +174,14 @@ public class DeliveryAssignmentService {
         return task;
     }
 
+    private void ensureNotAssigned(String bizType, Long bizOrderId) {
+        for (DeliveryOrderResponse task : tasks.values()) {
+            if (bizType.equals(task.getBizType()) && bizOrderId.equals(task.getBizOrderId())) {
+                throw new BizException("订单已派单");
+            }
+        }
+    }
+
     private void enrichAddressContact(DeliveryOrderResponse task, Long userId, Long addressId) {
         if (addressId == null) {
             return;
diff --git a/backend/src/test/java/com/linhelp/delivery/DeliveryAssignmentServiceTests.java b/backend/src/test/java/com/linhelp/delivery/DeliveryAssignmentServiceTests.java
index 8fc8f50..d20bdd0 100644
--- a/backend/src/test/java/com/linhelp/delivery/DeliveryAssignmentServiceTests.java
+++ b/backend/src/test/java/com/linhelp/delivery/DeliveryAssignmentServiceTests.java
@@ -69,6 +69,18 @@ class DeliveryAssignmentServiceTests {
                 .hasMessageContaining("自提订单无需派单");
     }
 
+    @Test
+    void cannotAssignSameGoodsOrderTwice() {
+        TestFixture fixture = new TestFixture();
+        GoodsOrderResponse order = fixture.preparedDeliveryOrder();
+        DeliveryUserResponse rider = fixture.rider();
+
+        fixture.assignmentService.assignGoodsOrder(order.getId(), rider.getId());
+
+        assertThatThrownBy(() -> fixture.assignmentService.assignGoodsOrder(order.getId(), rider.getId()))
+                .hasMessageContaining("订单已派单");
+    }
+
     private static class TestFixture {
         private final ProductService productService = new ProductService();
         private final GoodsOrderService goodsOrderService = new GoodsOrderService(productService);