父:

<template>
    <div class="home">
        <p>父: {{num}}</p>
        <MChild v-model="num"></MChild>
    </div>
</template>

<script>
    import MChild from "../components/MChild/index.vue"
    export default {
        name: 'home',
        data() {
            return {
                num: 1
            }
        },
        components: {
            MChild
        }
    }
</script>

子:

<template>
    <div class="child">
        <p>子: {{num}}</p>
        <a href="javascript:;" @click="handleAdd">点击+1</a>
    </div>
</template>

<script>
    export default {
        props: {
            num: Number
        },
        model: {
            prop: 'num',
            event: 'add'
        },
        methods: {
            handleAdd() {
                this.$emit('add', ++this.num);
            }
        }
    }
</script>