<h4 class="relative">
   <a href="javascript:;">你的二维码
      <div class="qrtip pos_ct">
         <img src="二维码地址" >
      </div>
   </a>
</h4>

样式

.relative {
  position: relative;
}

.relative .qrtip {
  position: absolute;
  padding: 5px;
  border-radius: 5px;
  width: 200px;
  height: 200px;
  background: #fff;
  text-align: center;
  display: none;
}

.relative a:hover .qrtip {
  display: block;
}

.relative .qrtip:before {
  content: "";
  width: 0;
  height: 0;
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent;
  border-right: 10px solid #fff;
  position: absolute;
}

.relative .qrtip.pos_ct:before {
  left: 100px;
  bottom: -15px;
  transform: rotate(270deg);
}

.relative .qrtip img {
  width: 95%;
}