用这种方法试试

option = {
  xAxis: {
    type: "category",
    data: ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
  },
  yAxis: {},
  series: [{
    data: [820, 932, 901, 934, 1290, 1330, 1320],
    type: "line",
    areaStyle:{
      opacity: 0.8,
      color: {
        type: 'linear',
        x: 0,
        y: 0,
        x1: 0,
        y1: 1,
        colorStops: [
          {
            offset: 0,
            color:'rgb(255, 0, 135, 0.1)'
          }, 
          {
            offset: 1,
            color:'rgb(255, 0, 135, 1)'
          }, 
          ]
      }
    }
  }]
}

参考文档：配置项手册