用ajax技术来实现用户名和密码的验证，不必另起页面。

1. [代码]ajax主体部分    

var xmlrequest;
function createXMLHttpRequest(){
           if(window.XMLHttpRequest){
              xmlrequest=new XMLHttpRequest();
           }
           else if(window.ActiveXObject){
                  try{
                     xmlrequest=new ActiveXObject("Msxm12.XMLHTTP");
                  }
                  catch(e){
                       try{
                         xmlrequest=new ActiveXObject("Microsoft.XMLHTTP");
                       }
                       catch(e){}
                  }
           
           }
}
function login(){     
  createXMLHttpRequest();
    var user = document.getElementById("yhm").value;
    var password = document.getElementById("mm").value;
    if(user==""||password==""){
      alert("请输入用户名和密码!");
      return false;
    }
    var url = "check.php?user="+user+"&password="+password;
    xmlrequest.open("POST",url,true);
    xmlrequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
     xmlrequest.onreadystatechange = function(){
    if(xmlrequest.readyState == 4){
      if(xmlrequest.status==200){
            var msg = xmlrequest.responseText;      
               if(msg=='1'){
                alert('用户名或密码错误!');
                user="";
                password="";
                return false;
            } 
            else{              
                window.location.href="index1.html";
            }
        }
    }
  }
    xmlrequest.send("user="+user+"&password="+password);
  }

2. [代码]html代码    

	<input  placeholder="用户名" autofocus="" type="text"name="username">   
        <input  placeholder="密码"  type="password" name="password">
        <button  id="dl" onclick="login()">登录</button>

3. [代码]这里用的是sha1加密,把你的密码和数据库名称修改成你自己的即可    

<?php
$yhm1=$_POST['user'];
 $mm1=$_POST['password'];
@ $dp=new mysqli('localhost','root','你的密码','你的数据库名称');
$yhm2=sha1($yhm1);
$mm2=sha1($mm1);
$query="select * from zhuce where yhm='$yhm2' and mm='$mm2'";
$result=$dp->query($query);
$num=$result->num_rows;
if(!$num){
    echo "1";
}

$dp->close();

?>