diff --git a/src/__tests__/lib/alipay/sign.test.ts b/src/__tests__/lib/alipay/sign.test.ts
index 74c17e8..5be2995 100644
--- a/src/__tests__/lib/alipay/sign.test.ts
+++ b/src/__tests__/lib/alipay/sign.test.ts
@@ -44,11 +44,16 @@ describe('Alipay RSA2 Sign', () => {
       expect(sign1).toBe(sign2);
     });
 
-    it('should filter out sign and sign_type fields', () => {
-      const paramsWithSign = { ...testParams, sign: 'old_sign', sign_type: 'RSA2' };
+    it('should filter out sign field but keep sign_type', () => {
+      const paramsWithSign = { ...testParams, sign: 'old_sign' };
       const sign1 = generateSign(testParams, privateKey);
       const sign2 = generateSign(paramsWithSign, privateKey);
       expect(sign1).toBe(sign2);
+
+      // sign_type should be included in signing
+      const paramsWithSignType = { ...testParams, sign_type: 'RSA2' };
+      const sign3 = generateSign(paramsWithSignType, privateKey);
+      expect(sign3).not.toBe(sign1);
     });
 
     it('should filter out empty values', () => {
diff --git a/src/lib/alipay/client.ts b/src/lib/alipay/client.ts
index acc1aee..7004b9e 100644
--- a/src/lib/alipay/client.ts
+++ b/src/lib/alipay/client.ts
@@ -51,7 +51,7 @@ export function pageExecute(
 
   params.sign = generateSign(params, env.ALIPAY_PRIVATE_KEY);
 
-  const query = new URLSearchParams({ ...params, sign_type: 'RSA2' }).toString();
+  const query = new URLSearchParams(params).toString();
   return `${GATEWAY}?${query}`;
 }
 
@@ -72,7 +72,6 @@ export async function execute<T extends AlipayResponse>(
   };
 
   params.sign = generateSign(params, env.ALIPAY_PRIVATE_KEY);
-  params.sign_type = 'RSA2';
 
   const response = await fetch(GATEWAY, {
     method: 'POST',
diff --git a/src/lib/alipay/sign.ts b/src/lib/alipay/sign.ts
index 5b51e48..d1c025c 100644
--- a/src/lib/alipay/sign.ts
+++ b/src/lib/alipay/sign.ts
@@ -14,9 +14,7 @@ function formatPublicKey(key: string): string {
 /** 生成 RSA2 签名 */
 export function generateSign(params: Record<string, string>, privateKey: string): string {
   const filtered = Object.entries(params)
-    .filter(
-      ([key, value]) => key !== 'sign' && key !== 'sign_type' && value !== '' && value !== undefined && value !== null,
-    )
+    .filter(([key, value]) => key !== 'sign' && value !== '' && value !== undefined && value !== null)
     .sort(([a], [b]) => a.localeCompare(b));
 
   const signStr = filtered.map(([key, value]) => `${key}=${value}`).join('&');
@@ -29,9 +27,7 @@ export function generateSign(params: Record<string, string>, privateKey: string)
 /** 用支付宝公钥验证签名 */
 export function verifySign(params: Record<string, string>, alipayPublicKey: string, sign: string): boolean {
   const filtered = Object.entries(params)
-    .filter(
-      ([key, value]) => key !== 'sign' && key !== 'sign_type' && value !== '' && value !== undefined && value !== null,
-    )
+    .filter(([key, value]) => key !== 'sign' && value !== '' && value !== undefined && value !== null)
     .sort(([a], [b]) => a.localeCompare(b));
 
   const signStr = filtered.map(([key, value]) => `${key}=${value}`).join('&');