<script type="text/javascript" src="jquery-3.0.0.js"></script>
<script type="text/javascript">
   $(function() {
    //獲取所有l(wèi)i遍歷
    $(".li_list").each(function() {
     //當(dāng)鼠標(biāo)進(jìn)去當(dāng)前l(fā)i
     $(this).mouseenter(function() {
      //設(shè)置當(dāng)前元素寬度
      $(this).stop()
        .animate({ "width": "600px" }, 500, "linear");
        //設(shè)置同胞元素寬度
        .siblings().stop()
           .animate({ "width": "100px" }, 500, "linear");
     });
    });
   });
  </script>

 .li_list {
    width: 100px;
    height: 300px;
    list-style: none;
    float: left;
    overflow: hidden;
   }

   .li_list img {
    width: 100%;
    height: 100%;
   }

   .divbg {
    width: 600px;
    height: 300px;
    background: rgba(230, 0, 0, 0.5);
    text-align: center;
    line-height: 300px;
    float: left;
   }

   .divbg span {
    display: block;
    width: 100px;
    height: 300px;
    float: left;
   }

   .div1 {
    width: 500px;
    height: 300px;
    float: left;
   }
   .mo{
    width: 600px;
   }

<ul class="ul_list">
   <li class="li_list">
    <div class="divbg">
     <span>萌寵</span>
     <div class="div1">
      <img src="img/0.jpg" />
     </div>
    </div>
   </li>
   <li class="li_list">
    <div class="divbg">
     <span>萌寵</span>
     <div class="div1">
      <img src="img/1.jpg" />
     </div>
    </div>
   </li>
   <li class="li_list">
    <div class="divbg">
     <span>萌寵</span>
     <div class="div1">
      <img src="img/2.jpg" />
     </div>
    </div>
   </li>
   <li class="li_list mo">
    <div class="divbg">
     <span>萌寵</span>
     <div class="div1">
      <img src="img/3.jpg" />
     </div>
    </div>
   </li>
  </ul>