关键:    position: fixed;

wxml:

<navigator url="/pages/issue/index">
<image class='img' src='/assets/images/Home/add.png' bindtap='add'></image>
</navigator>

wxss:

.img{
float: right;
position: fixed;
bottom: 120rpx;
right: 20rpx;
width: 80rpx;
height: 80rpx;
}

js:

add(e){
console.log(e);
},

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