加个left层吧
HTML 代码:
<html><head><title>css</title><style type="text/css">
#left {float:left;}
#up {background-color:red;width:100px;height:100px;float:left;}
#down {background-color:red;width:100px;height:100px;clear:left;margin-top:10px;float:left;}
#right {background-color:red;width:100px;height:210px;float:left;margin-left:10px;}
</style>
</head>
<body>
<div id="left">
<div id="up"></div>
<div id="down"></div>
</div>
<div id="right"></div>
</body>
</html>