确保img的宽高比固定

html:

<div class="wrapper">
        <swiper :options="swiperOption">
                <swiper-slide>
                    <img class="swiper-img" src="http://img1.qunarzz.com/piao/fusion/1811/7c/8e5c4ab8ee8b7402.jpg_750x200_dd7a38dd.jpg" alt="">
                </swiper-slide>
                <swiper-slide>
                    <img class="swiper-img" src="http://img1.qunarzz.com/piao/fusion/1811/a8/cb43c4ac6c215d02.jpg_750x200_83dee994.jpg" alt="">
                </swiper-slide>
                <div class="swiper-pagination"  slot="pagination"></div>
        </swiper>
</div>

css

第一种方法：

wrapper{
 width:100%;
 height:31.25vw
}

第二种方法：

wrapper{
 overflow: hidden；
 width: 100%；
 height: 0；
 padding-bottom: 31.25%；
}

31.25%为固定宽高比