diff --git a/backend/services/planting-service/src/pre-planting/application/services/pre-planting-application.service.ts b/backend/services/planting-service/src/pre-planting/application/services/pre-planting-application.service.ts
index 995415d2..0bcf7c9f 100644
--- a/backend/services/planting-service/src/pre-planting/application/services/pre-planting-application.service.ts
+++ b/backend/services/planting-service/src/pre-planting/application/services/pre-planting-application.service.ts
@@ -574,18 +574,24 @@ export class PrePlantingApplicationService {
     accountSequence: string,
     position: import('../../domain/aggregates/pre-planting-position.aggregate').PrePlantingPosition,
   ) {
-    // 获取待合并的已支付订单（数量由 PRE_PLANTING_PORTIONS_PER_TREE 决定）
-    const paidOrders = await this.orderRepo.findPaidOrdersByUserId(
-      tx,
-      userId,
-      PRE_PLANTING_PORTIONS_PER_TREE,
-    );
+    // 获取所有已支付订单，按份数累加取够 PRE_PLANTING_PORTIONS_PER_TREE 份
+    // 注意：一笔订单可能包含多份（portionCount > 1），所以不能按订单条数判断
+    const allPaidOrders = await this.orderRepo.findPaidOrdersByUserId(tx, userId);
 
-    if (paidOrders.length < PRE_PLANTING_PORTIONS_PER_TREE) {
-      throw new Error(`不足 ${PRE_PLANTING_PORTIONS_PER_TREE} 笔已支付订单进行合并`);
+    let accumulatedPortions = 0;
+    const sourceOrders: typeof allPaidOrders = [];
+    for (const order of allPaidOrders) {
+      sourceOrders.push(order);
+      accumulatedPortions += order.portionCount;
+      if (accumulatedPortions >= PRE_PLANTING_PORTIONS_PER_TREE) break;
+    }
+
+    if (accumulatedPortions < PRE_PLANTING_PORTIONS_PER_TREE) {
+      throw new Error(
+        `不足 ${PRE_PLANTING_PORTIONS_PER_TREE} 份进行合并（当前 ${accumulatedPortions} 份，来自 ${sourceOrders.length} 笔订单）`,
+      );
     }
 
-    const sourceOrders = paidOrders.slice(0, PRE_PLANTING_PORTIONS_PER_TREE);
     const sourceOrderNos = sourceOrders.map((o) => o.orderNo);
     const mergeNo = this.generateMergeNo();
 
diff --git a/backend/services/planting-service/src/pre-planting/domain/aggregates/pre-planting-merge.aggregate.ts b/backend/services/planting-service/src/pre-planting/domain/aggregates/pre-planting-merge.aggregate.ts
index fd3d2301..68c44d87 100644
--- a/backend/services/planting-service/src/pre-planting/domain/aggregates/pre-planting-merge.aggregate.ts
+++ b/backend/services/planting-service/src/pre-planting/domain/aggregates/pre-planting-merge.aggregate.ts
@@ -70,8 +70,8 @@ export class PrePlantingMerge {
     cityCode: string,
     totalTreesMergedAfter: number,
   ): PrePlantingMerge {
-    if (sourceOrderNos.length !== PRE_PLANTING_PORTIONS_PER_TREE) {
-      throw new Error(`合并需要 ${PRE_PLANTING_PORTIONS_PER_TREE} 个订单，收到 ${sourceOrderNos.length} 个`);
+    if (sourceOrderNos.length === 0) {
+      throw new Error('合并至少需要 1 笔源订单');
     }
 
     const merge = new PrePlantingMerge(
diff --git a/backend/services/planting-service/src/pre-planting/infrastructure/repositories/pre-planting-order.repository.ts b/backend/services/planting-service/src/pre-planting/infrastructure/repositories/pre-planting-order.repository.ts
index c8baf0dd..457670d8 100644
--- a/backend/services/planting-service/src/pre-planting/infrastructure/repositories/pre-planting-order.repository.ts
+++ b/backend/services/planting-service/src/pre-planting/infrastructure/repositories/pre-planting-order.repository.ts
@@ -61,12 +61,10 @@ export class PrePlantingOrderRepository {
   async findPaidOrdersByUserId(
     tx: Prisma.TransactionClient,
     userId: bigint,
-    limit: number,
   ): Promise<PrePlantingOrder[]> {
     const records = await tx.prePlantingOrder.findMany({
       where: { userId, status: PrePlantingOrderStatus.PAID },
       orderBy: { createdAt: 'asc' },
-      take: limit,
     });
     return records.map((r) => this.toDomain(r));
   }