index.php

<html>
<head>
<meta charset="UTF-8">
<title>Ajax+PHP</title>
<script type="text/javascript" src="https://code.jquery.com/jquery-3.0.0.min.js"></script>
</head>
<body>
	用户名:<input type="text" id='username' name="username" /></br>
	密    码:<input type="password" id='password' name="password" /></br>
	<input type='button' class="but" value="ajax提交"/>
	<span class="content"></span>
	<script type="text/javascript">
		$(document).ready(function(){

			$(".but").click(function(){
				var username =$("#username").val();
				var password =$("#password").val();
				$.ajax({
					url: "ajax.php",
					type: "POST",
					data:{name:username,pwd:password},
					dataType:'json',
					error: function(){
						 alert('Error loading XML document'); 
					},
					success:function(data,status){
				    alert(status);
				    alert(data);
						$('.content').html("用户名:"+data[0]+"密码:"+data[1]);
					}
				})
			})
		})
	</script>
</body>
</html>

　ajax.php

<?php 
$name = $_POST['name'];
$pwd = $_POST['pwd'];
$array = array("$name","$pwd");
//这里进行一个些操作，比如数据库交互
 
echo json_encode($array);//json_encode方式是必须的
?>