已经解决,还是要利用canvas原生解决方案,读取文件base64

function coverCanvas() {
  var headCoUrl = 'cloud://****18635e09448b.jpg';
  query.select('#myCanvas')
    .fields({
      node: true,
      size: true
    })
    .exec(async function () {
      let canvas = res[0].node;
      let ctx = canvas.getContext('2d');
      let imgOb = canvas.createImage();


      canvas.width = 100;
      canvas.height = 100;
      imgOb.onload = () => {
        // run other
      }
      imgOb.onerror = err=>{
      }
      imgOb.src = await loadImage(headCoUrl);
    });


  function loadImage(cloudUrl) {
    return Promise((resolve, reject) => {
      wx.cloud.downloadFile({
        fileID: cloudUrl,
        success: res => {
        
          //重点来了
          let fs = wx.getFileSystemManager();
          fs.readFile({
            filePath: res.tempFilePath,
            encoding:'base64',
            success: function(res){
              console.log(res);
              pm.resolve(`data:image/png;base64,${res.data}`)
            }
          })
          resolve(res.tempFilePath)
        },
        fail: res => reject
      });
    });
  }
}