diff --git a/WePayV3/Cert.php b/WePayV3/Cert.php
index edede32..bd5c7f9 100644
--- a/WePayV3/Cert.php
+++ b/WePayV3/Cert.php
@@ -42,13 +42,14 @@ class Cert extends BasicWePay
     public function download()
     {
         try {
-            $aes = new DecryptAes($this->config['mch_v3_key']);
-            $result = $this->doRequest('GET', '/v3/certificates');
             $certs = [];
+            $result = $this->doRequest('GET', '/v3/certificates');
+            $decrypt = new DecryptAes($this->config['mch_v3_key']);
             foreach ($result['data'] as $vo) {
                 $certs[$vo['serial_no']] = [
                     'expire'  => strtotime($vo['expire_time']),
-                    'content' => $aes->decryptToString(
+                    'serial'  => $vo['serial_no'],
+                    'content' => $decrypt->decryptToString(
                         $vo['encrypt_certificate']['associated_data'],
                         $vo['encrypt_certificate']['nonce'],
                         $vo['encrypt_certificate']['ciphertext']
diff --git a/WePayV3/Contracts/BasicWePay.php b/WePayV3/Contracts/BasicWePay.php
index 798b707..f0908f0 100644
--- a/WePayV3/Contracts/BasicWePay.php
+++ b/WePayV3/Contracts/BasicWePay.php
@@ -367,35 +367,28 @@ abstract class BasicWePay
     protected function _getCert($serial = '')
     {
         $certs = $this->tmpFile("{$this->config['mch_id']}_certs");
-        if (empty($certs) || empty($certs[$serial]['content'])) {
+        if (empty($certs) || empty($certs[$serial]['serial']) || empty($certs[$serial]['content'])) {
             Cert::instance($this->config)->download();
             $certs = $this->tmpFile("{$this->config['mch_id']}_certs");
         }
         foreach ($certs as $cert) {
-            if ($certs[$serial]['expire'] > time()) {
+            if (!empty($cert['serial']) && !empty($cert['content']) && $cert['expire'] > time()) {
                 $this->config['cert_package'][$cert['serial']] = $cert['content'];
-                if (empty($this->config['mp_cert_serial'])) {
+                if (empty($this->config['mp_cert_serial']) && (empty($serial) || $serial === $cert['serial'])) {
                     $this->config['mp_cert_serial'] = $cert['serial'];
                     $this->config['mp_cert_content'] = $cert['content'];
                 }
             }
         }
-        // 未设置序号时，直接返回默认证书内容
-        if (empty($serial) && !empty($this->config['mp_cert_content'])) {
+        if (isset($this->config['cert_package'][$serial])) {
+            return $this->config['cert_package'][$serial];
+        } elseif (!empty($this->config['mp_cert_content'])) {
             return $this->config['mp_cert_content'];
-        }
-
-        // 遍历证书数组，找到匹配的证书
-        if ($cert = $this->withCertPayment()) {
+        } elseif ($cert = $this->withCertPayment()) {
             return $cert;
-        }
-
-        // 检查指定序号的证书是否存在
-        if (!isset($this->config['cert_package'][$serial])) {
+        } else {
             throw new InvalidResponseException("读取平台证书失败！");
         }
-
-        return $this->config['cert_package'][$serial];
     }
 
     /**