nth-of-type

<view class="upload_lists">


        <view class="upload_btn">
          　　<view class="camera"></view>
          　　<view class="upload_words">点击上传</view>
      </view>



      <view class="upload_btn">
          　　<view class="camera"></view>
          　　<view class="upload_words">点击上传</view>
      </view>



      <view class="upload_btn">
          　　<view class="camera"></view>
          　　<view class="upload_words">点击上传</view>
      </view>
    </view>




  </view>

.upload_lists .upload_btn:nth-of-type(3n+2){
　　margin-left:38rpx;
}

锁定class 为 upload_btn 的第2 5 8 ....个元素  , 前面要加个 .upload_lists 来限制,否则如果页面其他地方也有 upload_btn 会出现比较操蛋的效果!