diff --git a/lastleg-service/src/main/java/com/baiyue/lastleg/dispatch/service/DispatchService.java b/lastleg-service/src/main/java/com/baiyue/lastleg/dispatch/service/DispatchService.java
index 4103f9045..ab620e3e3 100644
--- a/lastleg-service/src/main/java/com/baiyue/lastleg/dispatch/service/DispatchService.java
+++ b/lastleg-service/src/main/java/com/baiyue/lastleg/dispatch/service/DispatchService.java
@@ -211,7 +211,7 @@ public class DispatchService {
             if (existing.size() > 1) throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "存在多个装车分组，请明确选择目标分组");
             if (existing.size() == 1) boundContainer = existing.get(0);
             else {
-                boundContainer = new DispatchDraftContainer(); boundContainer.setId(IdWorker.getId()); boundContainer.setDraftId(draft.getId()); boundContainer.setDraftToken(request.draftToken()); boundContainer.setSequenceNo(1); boundContainer.setCapacity(500); boundContainer.setCreatedAt(LocalDateTime.now()); boundContainer.setUpdatedAt(LocalDateTime.now()); draftContainers.insert(boundContainer);
+                boundContainer = new DispatchDraftContainer(); boundContainer.setId(IdWorker.getId()); boundContainer.setDraftId(draft.getId()); boundContainer.setDraftToken(request.draftToken()); boundContainer.setSequenceNo(1); boundContainer.setCapacity(30); boundContainer.setCreatedAt(LocalDateTime.now()); boundContainer.setUpdatedAt(LocalDateTime.now()); draftContainers.insert(boundContainer);
             }
         }
         if (boundContainer == null || !request.draftToken().equals(boundContainer.getDraftToken()) || !Objects.equals(boundContainer.getDraftId(), draft.getId())) throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "装车托盘不存在");
@@ -335,7 +335,9 @@ public class DispatchService {
             actualGroups.add(container.getId());
             var group = groups.get(container.getId());
             if (group == null) throw new ResponseStatusException(HttpStatus.CONFLICT, "草稿分组已变化，请重新加载");
-            if (container.getCapacity() == null || bound.size() > container.getCapacity())
+            if (container.getCapacity() == null || !Set.of(15, 30).contains(container.getCapacity()))
+                throw new ResponseStatusException(HttpStatus.CONFLICT, "车辆大小仅支持15托或30托");
+            if (bound.size() > container.getCapacity())
                 throw new ResponseStatusException(HttpStatus.CONFLICT, "装车分组超过车型托位容量");
             Set<String> actual = new HashSet<>();
             Set<String> customers = new HashSet<>();
diff --git a/lastleg-service/src/main/resources/openapi/overseas-business-v1.yaml b/lastleg-service/src/main/resources/openapi/overseas-business-v1.yaml
index fd13c94b2..c86721ade 100644
--- a/lastleg-service/src/main/resources/openapi/overseas-business-v1.yaml
+++ b/lastleg-service/src/main/resources/openapi/overseas-business-v1.yaml
@@ -2808,7 +2808,7 @@ components:
         returnReceiptId: { type: string }
         sourceType: { type: string, enum: [INBOUND_PLAN, RETURN_RECEIPT] }
         draftToken: { type: string, minLength: 1, maxLength: 64 }
-        draftContainerId: { type: string, nullable: true, description: 托盘所在草稿车厢ID }
+        draftContainerId: { type: string, nullable: true, description: 托盘所在草稿车厢ID；省略时复用唯一分组，无分组则新建30托默认组，多组时必须明确选择 }
     SmartDispatchDraftRelease:
       type: object
       required: [draftToken]
diff --git a/lastleg-service/src/test/java/com/baiyue/lastleg/dispatch/service/DispatchServiceTest.java b/lastleg-service/src/test/java/com/baiyue/lastleg/dispatch/service/DispatchServiceTest.java
index 7367f9a75..8775a623b 100644
--- a/lastleg-service/src/test/java/com/baiyue/lastleg/dispatch/service/DispatchServiceTest.java
+++ b/lastleg-service/src/test/java/com/baiyue/lastleg/dispatch/service/DispatchServiceTest.java
@@ -163,6 +163,7 @@ class DispatchServiceTest {
         ArgumentCaptor<DispatchDraftContainer> group = ArgumentCaptor.forClass(DispatchDraftContainer.class);
         verify(draftContainers).insert(group.capture());
         assertNotNull(group.getValue().getId());
+        assertEquals(30, group.getValue().getCapacity());
         assertEquals(group.getValue().getId(), lock.getValue().getDraftContainerId());
         assertNotNull(lock.getValue().getExpiresAt());
         assertEquals(null, lock.getValue().getDispatchOrderId());
@@ -676,6 +677,40 @@ class DispatchServiceTest {
         verify(orders, never()).insert(any(DispatchOrder.class)); verify(items, never()).insert(any(DispatchItem.class));
     }
 
+    @Test
+    void groupedPreArrangeRejectsUnsupportedStoredCapacityBeforeCreatingDispatches() {
+        var fixture = twoGroupFixture();
+        for (Integer capacity : java.util.Arrays.asList(null, 0, 31, 500)) {
+            fixture.containers().get(0).setCapacity(capacity);
+            var error = assertThrows(ResponseStatusException.class,
+                () -> service.preArrangeDraft("7", fixture.request()));
+            assertEquals(409, error.getStatusCode().value());
+            assertEquals("车辆大小仅支持15托或30托", error.getReason());
+        }
+        verify(orders, never()).insert(any(DispatchOrder.class));
+        verify(items, never()).insert(any(DispatchItem.class));
+    }
+
+    @Test
+    void groupedPreArrangeRejectsThirtyOnePalletsInThirtyPalletVehicle() {
+        twoGroupFixture();
+        var palletIds = java.util.stream.LongStream.rangeClosed(100, 130).boxed().toList();
+        var bound = palletIds.stream().map(id -> {
+            var lock = new DispatchPalletLock();
+            lock.setPlanPalletId(id);
+            return lock;
+        }).toList();
+        when(locks.lockActiveByDraftContainer("draft-multi", 21L)).thenReturn(bound);
+        var request = new DispatchRequests.PreArrangeDraft("draft-multi",
+            List.of(new DispatchRequests.DraftGroup(21L, palletIds, List.of())));
+        var error = assertThrows(ResponseStatusException.class,
+            () -> service.preArrangeDraft("7", request));
+        assertEquals(409, error.getStatusCode().value());
+        assertEquals("装车分组超过车型托位容量", error.getReason());
+        verify(orders, never()).insert(any(DispatchOrder.class));
+        verify(items, never()).insert(any(DispatchItem.class));
+    }
+
     @Test
     void secondGroupFailureRollsBackFirstGroupInsertInTheSameTransaction() {
         var fixture = twoGroupFixture();