diff --git a/backend/apps/tickets/migrations/0003_repair_closed_resolved_flags.py b/backend/apps/tickets/migrations/0003_repair_closed_resolved_flags.py
new file mode 100644
index 0000000..3a2bce3
--- /dev/null
+++ b/backend/apps/tickets/migrations/0003_repair_closed_resolved_flags.py
@@ -0,0 +1,21 @@
+from django.db import migrations
+
+
+def repair_closed_resolved_flags(apps, schema_editor):
+    Ticket = apps.get_model("tickets", "Ticket")
+    Ticket.objects.filter(
+        status="closed",
+        resolved_at__isnull=False,
+        resolution_summary__gt="",
+        is_resolved=False,
+    ).update(is_resolved=True)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("tickets", "0002_ticket_context_and_standard_categories"),
+    ]
+
+    operations = [
+        migrations.RunPython(repair_closed_resolved_flags, migrations.RunPython.noop),
+    ]
diff --git a/backend/apps/tickets/services.py b/backend/apps/tickets/services.py
index 9cbaff0..89e03a8 100644
--- a/backend/apps/tickets/services.py
+++ b/backend/apps/tickets/services.py
@@ -95,7 +95,7 @@ def transition_ticket(
     if to_status == "resolved":
         ticket.resolved_at = timezone.now()
         ticket.is_resolved = True if is_resolved is None else is_resolved
-    elif is_resolved is not None:
+    elif to_status != "closed" and is_resolved is not None:
         ticket.is_resolved = is_resolved
     if to_status == "closed":
         ticket.closed_at = timezone.now()
diff --git a/backend/apps/tickets/tests/test_ticket_api.py b/backend/apps/tickets/tests/test_ticket_api.py
index dfa320c..8b10663 100644
--- a/backend/apps/tickets/tests/test_ticket_api.py
+++ b/backend/apps/tickets/tests/test_ticket_api.py
@@ -192,6 +192,28 @@ def test_technical_ticket_cannot_be_resolved_directly(admin_client, db):
     assert response.status_code == 400
 
 
+def test_closing_resolved_ticket_keeps_resolved_flag(admin_client, db):
+    ticket = Ticket.objects.create(
+        ticket_no="TK202607010106",
+        title="已解决待关闭",
+        description="A",
+        status="resolved",
+        is_resolved=True,
+        resolution_summary="已完成处理",
+    )
+
+    response = admin_client.post(
+        f"/api/tickets/{ticket.id}/status",
+        data={"status": "closed", "remark": "已回复", "is_resolved": False},
+        content_type="application/json",
+    )
+
+    assert response.status_code == 200
+    ticket.refresh_from_db()
+    assert ticket.status == "closed"
+    assert ticket.is_resolved is True
+
+
 def test_get_ticket_events_returns_real_timeline_with_operator(admin_client, db):
     user_model = get_user_model()
     operator = user_model.objects.get(username="admin")
diff --git a/frontend/src/features/tickets/TicketDetailPage.tsx b/frontend/src/features/tickets/TicketDetailPage.tsx
index 735e141..bc80417 100644
--- a/frontend/src/features/tickets/TicketDetailPage.tsx
+++ b/frontend/src/features/tickets/TicketDetailPage.tsx
@@ -90,7 +90,7 @@ export function TicketDetailPage({ ticketId }: { ticketId: number }) {
     values: {
       remark: string
       resolution: string
-      is_resolved: boolean
+      is_resolved?: boolean
       replied_to_customer: boolean
     }
   ) {
diff --git a/frontend/src/features/tickets/TicketTransitionDialog.tsx b/frontend/src/features/tickets/TicketTransitionDialog.tsx
index c4a9360..c005bbf 100644
--- a/frontend/src/features/tickets/TicketTransitionDialog.tsx
+++ b/frontend/src/features/tickets/TicketTransitionDialog.tsx
@@ -32,7 +32,7 @@ type TicketTransitionDialogProps = {
     values: {
       remark: string
       resolution: string
-      is_resolved: boolean
+      is_resolved?: boolean
       replied_to_customer: boolean
     }
   ) => Promise<void>
@@ -70,7 +70,7 @@ export function TicketTransitionDialog({
       await onSubmit(status, {
         remark: remark.trim(),
         resolution: resolution.trim(),
-        is_resolved: status === 'resolved',
+        is_resolved: status === 'resolved' ? true : undefined,
         replied_to_customer: repliedToCustomer
       })
       onOpenChange(false)