首先要保证语法没问题，然后好像和 throw new Exception和trigger_error 没关系了，上代码：

<?php

    function test($abc){
        mysql_connect("localhost", "用户名错误", "密码错误");
    }
    
    function test2($abc){
        mysql_connect("localhost", "用户名错误", "密码错误");
    }
    
    test("abc");
    @test2("abc");
?>

Warning: mysql_connect() [function.mysql-connect]: Access denied for user '用户名错误'@'localhost' (using password: YES) in D:Projectsns1.php on line 4

test2没有抛出 Warning.