SOURCE

Vue.component('parent-component',{
  template: `
		<div>
			<child-one-component @updateChildTwo="updateChildTwo">
    	</child-one-component>
			<child-two-component :msg="msg">
			</child-two-component>
		</div>
	`,
  data(){
    return {
      msg: 'child-two-component'
    }
  },
  methods:{
    updateChildTwo(){
      this.msg = "child-two 组件更新了";
    }
  }
});

Vue.component('child-one-component',{
  template: `
		<div>
			<button @click="updateChildTwo">child-one 更新兄弟组件</button>
		</div>
	`,
  methods:{
    updateChildTwo(){
      this.$emit('updateChildTwo')
    }
  }
});

Vue.component('child-two-component',{
  template: `
		<div>
			{{ msg }}
		</div>
	`,
  props: {
    msg: String,
  }
});

new Vue({
  el: '#root',
})

<script src="https://unpkg.com/vue"></script>

<div id="root">
  <parent-component>
  </parent-component>
</div>