Edit in JSFiddle

$(function(){
    //初始化设置
    var zIndex = 1;
    $('.div1').css('zIndex', zIndex);
    zIndex += 1;
    $('.div2').css('zIndex', zIndex);
    zIndex += 1;
    $('.div3').css('zIndex', zIndex);
    zIndex += 1;
    //窗体点击事件
    $('div').click(function(){
        $(this).css('zIndex', zIndex);
        zIndex += 1;
    });
});

<div class="div1"></div>
<div class="div2"></div>
<div class="div3"></div>

div{position:absolute;width:200px;height:100px;background:#fff}
.div1{top:100px;left:270px;background:red}
.div2{top:50px;left:240px;background:blue}
.div3{top:75px;left:300px;background:yellow}