这没有毛病啊，为什么会连接不上呢？

这是部分代码<?php

class ConnDB{
private $localhost;
private $username;

private $pwd;
private $dbname;
private $coon;
private $code;
function _construct($localhost,$username,$pwd,$dbname,$coon, $code){
    $this->localhost=$localhost;
    $this->username=$username;
    $this->pwd=$pwd;
    $this->dbname=$dbname;
    $this->code=$code;
}
function connect(){
    $this->conn=mysqli_connect($this->localhost,$this->username, $this->pwd,$this->dbname)or die("Connect MySQL False");
    mysqli_query($this->conn,"set names $this->code");
    return $this->conn;
    }

}

看一下你的php报错呀。

<?php
$con=mysqli_connect("localhost","wrong_user","my_password","my_db");
// 检查连接
if (!$con)
{
    die("连接错误: " . mysqli_connect_error());
}
?>