1、.clearfloat:after{
display:block;
clear:both;
content:"";
visibility:hidden;
height:0;
}
.clearfloat{zoom:1;//为了兼容IE}
2、在结尾处添加空div标签clear:both;
.clearfloat{clear:both;}
3、父级元素定义height
4、父级div定义overflow:hidden