其實很簡單:只需要設置div的margin值爲邊框值的相反數就行
.div {width:100px; height:103px; border:1px solid #333; margin-right:-1px; margin-bottom:-1px;}
.float-left{float:left;}
.clear-both{clear:both;}
<div class="div"></div>
<div class="div float-left"></div>
<div class="div float-left"></div>
<div class="div float-left"></div>
<div class="clear-both"></div>