1、运用css3的nth-child(3n):
<!DOCTYPE html><html><head> ???<meta charset="UTF-8"> ???<title>demo</title> ???<style> ???*{margin:0;padding:0} ???????.box{width:620px;padding:10px;background:#bbb;border:1px solid #f00;margin:0 auto;} ???????.box ul{overflow:hidden;} ???????.box ul li{list-style:none;width:200px;height:100px;background:#fff;float:left;margin-right:10px;margin-bottom:10px;} ???????.box ul li:nth-child(3n){margin-right:0;} ???</style></head><body><div class="box"> ???<ul> ???????<li>1</li> ???????<li>2</li> ???????<li>3</li> ???????<li>4</li> ???????<li>5</li> ???????<li>6</li> ???????<li>7</li> ???????<li>8</li> ???????<li>9</li> ???????<li>10</li> ???????<li>11</li> ???????<li>12</li> ???????<li>13</li> ???</ul></div></body></html>2、运用margin负值(该方法可以兼容老版浏览器):
<!DOCTYPE html><html><head> ???<meta charset="UTF-8"> ???<title>demo</title> ???<style> ???*{margin:0;padding:0} ???????.box{width:620px;padding:10px;background:#bbb;border:1px solid #f00;margin:0 auto;} ???????.box ul{overflow:hidden;margin-left:-10px;} ???????.box ul li{list-style:none;width:200px;height:100px;background:#fff;float:left;margin-left:10px;margin-bottom:10px;} ???</style></head><body><div class="box"> ???<ul> ???????<li>1</li> ???????<li>2</li> ???????<li>3</li> ???????<li>4</li> ???????<li>5</li> ???????<li>6</li> ???????<li>7</li> ???????<li>8</li> ???????<li>9</li> ???????<li>10</li> ???????<li>11</li> ???????<li>12</li> ???????<li>13</li> ???</ul></div></body></html>CSS解决ul下面最后一个li的margin
原文地址：http://www.cnblogs.com/web-wjg/p/7525712.html