diff --git a/library/think/Model.php b/library/think/Model.php
index 8ab7d1cb..53ad11f6 100644
--- a/library/think/Model.php
+++ b/library/think/Model.php
@@ -30,7 +30,7 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
     protected static $event = [];
 
     // 数据表主键 复合主键使用数组定义
-    protected $pk = 'id';
+    protected $pk;
     // 错误信息
     protected $error;
     // 当前模型名称
@@ -177,7 +177,7 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
      */
     public function getPk($table = '')
     {
-        if (!$this->pk) {
+        if (empty($this->pk)) {
             $this->pk = self::db()->getTableInfo($table, 'pk');
         }
         return $this->pk;
@@ -272,8 +272,9 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
             // 获取自动增长主键
             if ($result && $getInsertId) {
                 $insertId = self::db()->getLastInsID();
-                if (is_string($this->pk) && $insertId) {
-                    $this->data[$this->pk] = $insertId;
+                $pk       = $this->getPk();
+                if (is_string($pk) && $insertId) {
+                    $this->data[$pk] = $insertId;
                 }
             }
             // 新增回调
@@ -731,7 +732,7 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
     {
         // 记录当前关联信息
         $model      = $this->parseModel($model);
-        $localKey   = $localKey ?: $this->pk;
+        $localKey   = $localKey ?: $this->getPk();
         $foreignKey = $foreignKey ?: Loader::parseName($this->name) . '_id';
         return $this->relation->hasOne($model, $foreignKey, $localKey);
     }
@@ -765,7 +766,7 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
     {
         // 记录当前关联信息
         $model      = $this->parseModel($model);
-        $localKey   = $localKey ?: $this->pk;
+        $localKey   = $localKey ?: $this->getPk();
         $foreignKey = $foreignKey ?: Loader::parseName($this->name) . '_id';
         return $this->relation->hasMany($model, $foreignKey, $localKey);
     }
diff --git a/library/think/model/Merge.php b/library/think/model/Merge.php
index 4279f152..541334d4 100644
--- a/library/think/model/Merge.php
+++ b/library/think/model/Merge.php
@@ -184,7 +184,7 @@ class Merge extends Model
                     $table = is_int($key) ? self::db()->name($model)->getTable() : $model;
                     // 处理关联模型数据
                     $data = $this->parseData($name, $this->data);
-                    self::db()->table($table)->strict(false)->where($this->fk, $this->data[$this->pk])->update($data);
+                    self::db()->table($table)->strict(false)->where($this->fk, $this->data[$this->getPk()])->update($data);
                 }
                 // 新增回调
                 $this->trigger('after_update', $this);
@@ -238,7 +238,7 @@ class Merge extends Model
             $result = self::db()->delete($this->data);
             if ($result) {
                 // 获取主键数据
-                $pk = $this->data[$this->pk];
+                $pk = $this->data[$this->getPk()];
 
                 // 删除关联数据
                 foreach (static::$relationModel as $key => $model) {