<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
body{margin: 0;padding: 0}
.left{ 200px;height: 500px;background: #ccc;position:absolute;left:0;top: 0}
.middle{height: 500px;background: red;}
.right{ 300px;height: 500px;background: #ddd;position: absolute;right: 0;top:0;}
</style>
</head>
<div class="left">ss</div>
<div class="middle"></div>
<div class="right">dd</div>
</body>
</html>
用绝对定位，中间一块自适应宽度