使用缩放，

html

1 <div class="slim"></div>

css

 1 .slim{
 2   position: relative;      
 3 }
 4 
 5 .slim:after{
 6    content: "";
 7    position: absolute;
 8    top: 0;
 9    left: 0;
10     width: 100%;
11     height: 1px;
12     -webkit-tranform: scaleY(.5);
13      tranform: scaleY(.5);
14      background-color: #ebebeb;          
15 }

效果：上面是细线，下面是正常的1像素