方法一：
.clearfix:after {content:"."; display:block; height:0; clear:both; }
.clearfix { *zoom:1; }
方法二:
.clearfix:before,.clearfix:after {
content:"";
display:table;
}
.clearfix:after { clear:both; }/* For IE 6/7 (trigger hasLayout) */
.clearfix { zoom:1; }
原文：http://www.cnblogs.com/xiaotaiyang/p/3957809.html