SOURCE

new Vue({
  el: "#app",
	data: {
  	val: 0
  },
  methods: {
  	func() {
    	this.val = 50
    }
  }
});

<script src="https://cdn.bootcss.com/vue/2.6.10/vue.js"></script>
<script src="https://cdn.bootcss.com/element-ui/2.7.2/index.js"></script>
<div id="app">
 	<el-progress :text-inside="true" :stroke-width="18" :percentage="val"></el-progress>
	<button @click="func">click</button>
	<i></i><i></i><i></i>
</div>

@import url('//cdn.bootcss.com/element-ui/2.7.2/theme-chalk/index.css')