//限制图片尺寸
    limitFileWH(E_width, E_height, file) {
      let _this = this;
      let imgWidth = "";
      let imgHight = "";
      const isSize = new Promise(function(resolve, reject) {
        let width = E_width;
        let height = E_height;
        let _URL = window.URL || window.webkitURL;
        let img = new Image();
        img.onload = function() {
          imgWidth = img.width;
          imgHight = img.height;
          let valid = img.width == width && img.height == height;
          valid ? resolve() : reject();
        }
        img.src = _URL.createObjectURL(file);
      }).then(() => {
        return true;
      }, () => {
        _this.$message.warning({
          message: '上传文件的图片大小不合符标准,宽需要为' + E_width + 'px，高需要为' + E_height + 'px。当前上传图片的宽高分别为：' + imgWidth + 'px和' +
            imgHight + 'px',
          btn: false
        })
        this.$refs.upload.clearFiles();
        this.fileList=''
        return false;
      });
      return isSize
    },

再定义方法 给上传前钩子调用

    beforeAvatarUpload(file){
      //调用[限制图片尺寸]函数
      this.limitFileWH(1220, 500, file).then((res) => {
        console.log(res)
        file.isFlag = res
      })
    },

:before-upload="beforeAvatarUpload"