diff --git a/src/server/routes/api/downstreamApiKeys.test.ts b/src/server/routes/api/downstreamApiKeys.test.ts
index 8a59c30..cd5610d 100644
--- a/src/server/routes/api/downstreamApiKeys.test.ts
+++ b/src/server/routes/api/downstreamApiKeys.test.ts
@@ -314,6 +314,44 @@ describe('downstream api keys routes', () => {
     });
   });
 
+  it('rejects duplicate key update with conflict status', async () => {
+    const firstRes = await app.inject({
+      method: 'POST',
+      url: '/api/downstream-keys',
+      payload: {
+        name: 'dup-a',
+        key: 'sk-dup-key-001',
+      },
+    });
+    expect(firstRes.statusCode).toBe(200);
+
+    const secondRes = await app.inject({
+      method: 'POST',
+      url: '/api/downstream-keys',
+      payload: {
+        name: 'dup-b',
+        key: 'sk-dup-key-002',
+      },
+    });
+    expect(secondRes.statusCode).toBe(200);
+
+    const secondId = secondRes.json().item.id as number;
+    const duplicateUpdateRes = await app.inject({
+      method: 'PUT',
+      url: `/api/downstream-keys/${secondId}`,
+      payload: {
+        name: 'dup-b-updated',
+        key: 'sk-dup-key-001',
+      },
+    });
+
+    expect(duplicateUpdateRes.statusCode).toBe(409);
+    expect(duplicateUpdateRes.json()).toMatchObject({
+      success: false,
+      message: 'API key 已存在',
+    });
+  });
+
   it('returns summary, overview and trend aggregated from proxy logs', async () => {
     const inserted = await db.insert(schema.downstreamApiKeys).values({
       name: 'analytics-key',
diff --git a/src/server/routes/api/downstreamApiKeys.ts b/src/server/routes/api/downstreamApiKeys.ts
index 78afe1e..c48c273 100644
--- a/src/server/routes/api/downstreamApiKeys.ts
+++ b/src/server/routes/api/downstreamApiKeys.ts
@@ -20,13 +20,42 @@ function validateKeyShape(key: string): boolean {
   return key.startsWith('sk-') && key.length >= 6;
 }
 
-function looksLikeUniqueViolation(error: unknown): boolean {
-  const message = (error as Error | undefined)?.message || '';
-  if (runtimeDbDialect === 'postgres') {
-    return message.includes('duplicate key value violates unique constraint') &&
-           message.includes('downstream_api_keys_key_unique');
+type ErrorLike = {
+  message?: string;
+  code?: string | number;
+  cause?: unknown;
+};
+
+function getErrorChain(error: unknown): ErrorLike[] {
+  const chain: ErrorLike[] = [];
+  const seen = new Set<unknown>();
+  let current: unknown = error;
+  while (current && typeof current === 'object' && !seen.has(current)) {
+    seen.add(current);
+    chain.push(current as ErrorLike);
+    current = (current as ErrorLike).cause;
   }
-  return message.includes('UNIQUE constraint failed') && message.includes('downstream_api_keys.key');
+  return chain;
+}
+
+function looksLikeUniqueViolation(error: unknown): boolean {
+  const chain = getErrorChain(error);
+  if (runtimeDbDialect === 'postgres') {
+    return chain.some((entry) => {
+      const message = entry.message || '';
+      const code = String(entry.code || '');
+      return code === '23505'
+        || (message.includes('duplicate key value violates unique constraint')
+          && message.includes('downstream_api_keys_key_unique'));
+    });
+  }
+  return chain.some((entry) => {
+    const message = entry.message || '';
+    const code = String(entry.code || '');
+    return code === 'SQLITE_CONSTRAINT'
+      || code === 'SQLITE_CONSTRAINT_UNIQUE'
+      || (message.includes('UNIQUE constraint failed') && message.includes('downstream_api_keys.key'));
+  });
 }
 
 function normalizeBatchIds(raw: unknown): number[] {