diff --git a/app/Http/Controllers/Admin/PlatformOrderController.php b/app/Http/Controllers/Admin/PlatformOrderController.php
index 152ad44..43b80ea 100644
--- a/app/Http/Controllers/Admin/PlatformOrderController.php
+++ b/app/Http/Controllers/Admin/PlatformOrderController.php
@@ -56,6 +56,17 @@ class PlatformOrderController extends Controller
             $siteSubscription = SiteSubscription::query()->with(['merchant', 'plan'])->find($siteSubscriptionId);
         }
 
+        // 续费下单场景：若带了 site_subscription_id，但未显式指定 merchant/plan，则从订阅上补齐默认值。
+        // 目的：让“从订阅维度跳转到下单页”的链路更稳，不必每次手工二次选择。
+        if ($siteSubscription) {
+            if ((int) ($defaults['merchant_id'] ?? 0) <= 0) {
+                $defaults['merchant_id'] = (int) ($siteSubscription->merchant_id ?? 0);
+            }
+            if ((int) ($defaults['plan_id'] ?? 0) <= 0) {
+                $defaults['plan_id'] = (int) ($siteSubscription->plan_id ?? 0);
+            }
+        }
+
         return view('admin.platform_orders.form', [
             'merchants' => $merchants,
             'plans' => $plans,
diff --git a/tests/Feature/AdminPlatformOrderCreateDefaultsAutoFillFromSubscriptionTest.php b/tests/Feature/AdminPlatformOrderCreateDefaultsAutoFillFromSubscriptionTest.php
new file mode 100644
index 0000000..e2a597d
--- /dev/null
+++ b/tests/Feature/AdminPlatformOrderCreateDefaultsAutoFillFromSubscriptionTest.php
@@ -0,0 +1,69 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Merchant;
+use App\Models\Plan;
+use App\Models\SiteSubscription;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class AdminPlatformOrderCreateDefaultsAutoFillFromSubscriptionTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected function loginAsPlatformAdmin(): void
+    {
+        $this->seed();
+
+        $this->post('/admin/login', [
+            'email' => 'platform.admin@demo.local',
+            'password' => 'Platform@123456',
+        ])->assertRedirect('/admin');
+    }
+
+    public function test_create_form_should_autofill_merchant_and_plan_from_subscription_when_not_provided(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $merchant = Merchant::query()->firstOrFail();
+        $plan = Plan::query()->create([
+            'code' => 'po_defaults_autofill_from_sub_plan',
+            'name' => '创建订单默认值：从订阅补齐 merchant/plan 测试套餐',
+            'billing_cycle' => 'monthly',
+            'price' => 100,
+            'list_price' => 100,
+            'status' => 'active',
+            'sort' => 10,
+            'published_at' => now(),
+        ]);
+
+        $sub = SiteSubscription::query()->create([
+            'merchant_id' => $merchant->id,
+            'plan_id' => $plan->id,
+            'status' => 'activated',
+            'source' => 'manual',
+            'subscription_no' => 'SUB_AUTOFILL_0001',
+            'plan_name' => $plan->name,
+            'billing_cycle' => $plan->billing_cycle,
+            'period_months' => 1,
+            'amount' => 100,
+            'starts_at' => now()->subDay(),
+            'ends_at' => now()->addMonth(),
+            'activated_at' => now()->subDay(),
+        ]);
+
+        // 仅传 site_subscription_id，不传 merchant_id / plan_id
+        $url = '/admin/platform-orders/create?site_subscription_id=' . $sub->id . '&order_type=renewal';
+
+        $res = $this->get($url);
+        $res->assertOk();
+
+        // 应自动预选订阅所属站点/套餐
+        $res->assertSee('<option value="' . $merchant->id . '" selected>', false);
+        $res->assertSee('<option value="' . $plan->id . '" selected>', false);
+
+        // 订阅 hidden input 仍应存在
+        $res->assertSee('name="site_subscription_id" value="' . $sub->id . '"', false);
+    }
+}