diff --git a/library/think/Model.php b/library/think/Model.php
index a96c7d6e..561792aa 100644
--- a/library/think/Model.php
+++ b/library/think/Model.php
@@ -649,7 +649,7 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
         if (false === $this->trigger('before_write', $this)) {
             return false;
         }
-
+        $pk = $this->getPk();
         if ($this->isUpdate) {
             // 自动更新
             $this->autoCompleteData($this->update);
@@ -680,7 +680,6 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
                 $where = $this->updateWhere;
             }
 
-            $pk = $this->getPk();
             if (is_string($pk) && isset($data[$pk])) {
                 if (!isset($where[$pk])) {
                     unset($where);
@@ -710,10 +709,9 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
             $result = $this->db()->insert($this->data);
 
             // 获取自动增长主键
-            if ($result) {
+            if ($result && is_string($pk) && !isset($this->data[$pk])) {
                 $insertId = $this->db()->getLastInsID($sequence);
-                $pk       = $this->getPk();
-                if (is_string($pk) && $insertId) {
+                if ($insertId) {
                     $this->data[$pk] = $insertId;
                 }
             }