有查了一下，發現PHP環境為PHP 5.4.22，而Dedecms 5.7最好是在PHP 5.3下使用，一些函數在PHP 5.4下已經廢棄，導致了一些問題。

解決DedeCMS 5.7登錄后臺空白的解決辦法:

打開include/userlogin.class.php文件，找到function keepUser()

將代碼修改為如下：

function keepUser()
{
if($this->userID != ” && $this->userType != ”)
{
global $admincachefile,$adminstyle;
if(empty($adminstyle)) $adminstyle = ‘dedecms’;
/*@session_register($this->keepUserIDTag);*/
$_SESSION[$this->keepUserIDTag] = $this->userID;
/* @session_register($this->keepUserTypeTag);*/
$_SESSION[$this->keepUserTypeTag] = $this->userType;
/* @session_register($this->keepUserChannelTag);*/
$_SESSION[$this->keepUserChannelTag] = $this->userChannel;
/*@session_register($this->keepUserNameTag);*/
$_SESSION[$this->keepUserNameTag] = $this->userName;
/* @session_register($this->keepUserPurviewTag);*/
$_SESSION[$this->keepUserPurviewTag] = $this->userPurview;
/*@session_register($this->keepAdminStyleTag);*/
$_SESSION[$this->keepAdminStyleTag] = $adminstyle;
PutCookie(‘DedeUserID’, $this->userID, 3600 * 24, ‘/’);
PutCookie(‘DedeLoginTime’, time(), 3600 * 24, ‘/’);
$this->ReWriteAdminChannel();
return 1;
}

修改后保存，就OK了。