diff --git a/src/Pay/Client.php b/src/Pay/Client.php
index 61e54fcaa..633db93bd 100644
--- a/src/Pay/Client.php
+++ b/src/Pay/Client.php
@@ -145,6 +145,11 @@ public function request(string $method, string $url, array $options = []): Respo
         if (! empty($this->prependHeaders)) {
             $options['headers'] = array_merge($this->prependHeaders, $options['headers']);
         }
+        
+        //如果有加密字段，需要携带
+        if(! isset($options['headers']['Wechatpay-Serial']) && $serial = $this->merchant->getPlatformCertSerial()){
+            $options['headers']['Wechatpay-Serial'] = $serial;
+        }
 
         return new Response(
             $this->client->request($method, $url, $options),
diff --git a/src/Pay/Contracts/Merchant.php b/src/Pay/Contracts/Merchant.php
index 0e2bc440a..ada407231 100644
--- a/src/Pay/Contracts/Merchant.php
+++ b/src/Pay/Contracts/Merchant.php
@@ -25,4 +25,8 @@ public function getPlatformCert(string $serial): ?PublicKey;
      * @return PublicKey[]
      */
     public function getPlatformCerts(): array;
+
+    public function getPlatformCertSerial(): ?string;
+
+    public function setPlatformCertSerial(string $serial): static;
 }
diff --git a/src/Pay/Merchant.php b/src/Pay/Merchant.php
index 1da21300d..3d9a6fab8 100644
--- a/src/Pay/Merchant.php
+++ b/src/Pay/Merchant.php
@@ -21,6 +21,11 @@ class Merchant implements MerchantInterface
      */
     protected array $platformCerts = [];
 
+    /**
+     * @var string|null
+     */
+    protected ?string $platCertSerial = null;
+
     /**
      * @param  array<int|string, string|PublicKey>  $platformCerts
      *
@@ -63,6 +68,11 @@ public function getV2SecretKey(): ?string
         return $this->v2SecretKey;
     }
 
+    public function getPlatformCertSerial(): ?string
+    {
+        return $this->platCertSerial;
+    }
+
     public function getPlatformCert(string $serial): ?PublicKey
     {
         return $this->platformCerts[$serial] ?? null;
@@ -98,4 +108,11 @@ protected function normalizePlatformCerts(array $platformCerts): array
 
         return $certs;
     }
+
+    public function setPlatformCertSerial(string $serial): static
+    {
+         $this->platCertSerial = $serial;
+
+        return $this;
+    }
 }
diff --git a/src/Pay/Utils.php b/src/Pay/Utils.php
index ffd2f0f36..b9b662a04 100644
--- a/src/Pay/Utils.php
+++ b/src/Pay/Utils.php
@@ -168,8 +168,10 @@ protected function createSignature(string $message): string
      */
     public function createRsaEncrypt(string $plaintext, ?string $serial = null): string
     {
+        $serial = $serial ?? $this->merchant->getPlatformCertSerial();
         $platformCerts = $this->merchant->getPlatformCerts();
         $platformCert = $serial ? $this->merchant->getPlatformCert($serial) : reset($platformCerts);
+
         if (empty($platformCert)) {
             throw new InvalidConfigException('Missing platform certificate.');
         }
@@ -177,6 +179,8 @@ public function createRsaEncrypt(string $plaintext, ?string $serial = null): str
         if (!openssl_public_encrypt($plaintext, $encrypted, $platformCert, OPENSSL_PKCS1_OAEP_PADDING)) {
             throw new EncryptionFailureException('Encrypt failed.');
         }
+        
+        $this->merchant->setPlatformCertSerial($serial ?? key($platformCerts));
 
         return base64_encode($encrypted);
     }
diff --git a/tests/Pay/UtilsTest.php b/tests/Pay/UtilsTest.php
index 7b9bdf9ec..2ab5034d3 100644
--- a/tests/Pay/UtilsTest.php
+++ b/tests/Pay/UtilsTest.php
@@ -81,12 +81,18 @@ public function test_create_rsa_encrypt()
             ]
         );
          $utils = new Utils(merchant: $merchant);
+         $this->assertSame(null,$merchant->getPlatformCertSerial());
          $this->assertIsString($utils->createRsaEncrypt('mock-plaintext', 'PUB_KEY_ID_123456'));
+         $this->assertSame('PUB_KEY_ID_123456',$merchant->getPlatformCertSerial());
+
          $this->assertIsString($utils->createRsaEncrypt('mock-plaintext'));
+         $this->assertSame('PUB_KEY_ID_123456',$merchant->getPlatformCertSerial());
+
          $this->expectException(InvalidConfigException::class);
          $utils->createRsaEncrypt('mock-plaintext', 'PUB_KEY_ID_456789');
-         $this->expectException(EncryptionFailureException::class);
-         $utils->createRsaEncrypt('', 'PUB_KEY_ID_123456');
-         
+
+        $this->expectException(EncryptionFailureException::class);
+        $utils->createRsaEncrypt(str_repeat('A', 256), 'PUB_KEY_ID_123456');
+
     }
 }