progress组件percent属性值动态数据渲染无效

uploadTask.onProgressUpdate(res => {  
                that.progress = res.progress;  
                that.progress = that.progress + '%';  
                console.log(that.progress);  
            });  

<progress :percent="progress" activeColor="#16BF23" stroke-width="3" />
为什么渲染不出来哪里出错了，求解