方法挺简单的

<template>
    <Input v-model="value" placeholder="微信内部号码" type="number" number="true" class="aaaa"  :maxlength="20" clearable style="width:80%;ime-mode:Disabled" @on-keydown="changeaa(event)">
      <span slot="prepend">微信</span>
     </Input>
</template>
<script>
    export default {
        data () {
            return {
                value: ''
            }
        },
      methods:{
        changeaa(event){
            //禁止非数字字符输入
          if(event.keyCode<48||event.keyCode>57)event.returnValue=false;
        }
      }
    }
</script>
<style>
.aaaa input::-webkit-outer-spin-button,
.aaaa input::-webkit-inner-spin-button {
    -webkit-appearance: none;
}
.aaaa input[type="number"] {
    -moz-appearance: textfield;
}
</style>

input type="number"很重要，防止中文输入法输入出现错误问题，如果右侧上下箭头没有去掉，请试着加下/deep/

/deep/.aaaa input::-webkit-outer-spin-button,
/deep/.aaaa input::-webkit-inner-spin-button {
    -webkit-appearance: none;
}
/deep/.aaaa input[type="number"] {
    -moz-appearance: textfield;
}

如果获取不到event，请试下$event

<template>
    <Input v-model="value" placeholder="微信内部号码" type="number" number="true" class="aaaa"  :maxlength="20" clearable style="width:80%;ime-mode:Disabled" @on-keydown="changeaa($event)">
      <span slot="prepend">微信</span>
     </Input>
</template>