直接上代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "![]()
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="![]()
http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>关于图片自适应div大小问题</title>
<style>
.img{
overflow: auto;
text-align: center;
height: 200px; 90%;
margin:0 auto 20px;
border-radius: 0px;
background-repeat: no-repeat;
background-position: center top;
-webkit-background-size: 100% 200px;
background-size: 100% 200px;
border:1px solid red;
}
</style>
</head>
<body>
<div class="img" style="background-image:url(../image/5.png)">
</div>
<script>
</script>
</body>
</html>
<html xmlns="
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>关于图片自适应div大小问题</title>
<style>
.img{
overflow: auto;
text-align: center;
height: 200px; 90%;
margin:0 auto 20px;
border-radius: 0px;
background-repeat: no-repeat;
background-position: center top;
-webkit-background-size: 100% 200px;
background-size: 100% 200px;
border:1px solid red;
}
</style>
</head>
<body>
<div class="img" style="background-image:url(../image/5.png)">
</div>
<script>
</script>
</body>
</html>
备注：-webkit-background-size：width、height
此属性意思是将图片宽度自适应屏幕，高度是200px,高度也是可以设置为百分比的。这最适合做移动端适配问题。当然要配合其他代码使用。