php无法远程连接mongodb的问题

try { 
    $this->_mongo = new MongoClient('mongodb://root:123456@192.168.1.222/admin'); 
        }catch(MongoConnectionException $e) { 
exit("Failed to connect to database :".$e->getMessage()); 
}

报错MongoDB::__construct(): invalid name
Failed to connect to database :Failed to connect to: 116.255.205.150:27017: send_package: error reading from socket: Unknown error
手册看了几遍参数应该是对的啊。
把ip改成错误的ip 就 Failed to connect to: 192.168.1.22:27017: Timed out after 1000 ms
换成正确的ip就报MongoDB::__construct(): invalid name，是什么原因？