实现echarts折线图内容区域渐变，需要在series中进行配置。areaStyle：区域填充样式。设置后显示成区域面积图。

示例代码：

series: [
  {
    type: "line",
    name: this.legendData[0],
    color: "#E3FF34",
    symbolSize: 14,
    symbol: "circle",
    showSymbol: false,
    data: this.echartData1,
    smooth: true,
    itemStyle: {
      shadowColor: "#ffffff",
      shadowBlur: 5,
    },
    areaStyle: {
      normal: {
        //颜色渐变函数 前四个参数分别表示四个位置依次为左、下、右、上
        color: new echarts.graphic.LinearGradient(0, 0, 0, 1, [
          {
            offset: 0,
            color: "rgba(227, 255, 52, 0.2)", // 0% 处的颜色
          },
          {
            offset: 1,
            color: "rgba(227, 255, 52, 0)", // 100% 处的颜色
          },
        ]), //背景渐变色
      },
    },
    lineStyle: {
      // 系列级个性化折线样式
      width: 4,
      type: "solid",
      color: "#E3FF34",
    },
  },
  {
    type: "line",
    name: this.legendData[1],
    color: "#00A3FF",
    symbolSize: 14,
    symbol: "circle",
    showSymbol: false,
    data: this.echartData2,
    smooth: true,
    itemStyle: {
      shadowColor: "#ffffff",
      shadowBlur: 5,
    },
    areaStyle: {
      normal: {
        //颜色渐变函数 前四个参数分别表示四个位置依次为左、下、右、上
        color: new echarts.graphic.LinearGradient(0, 0, 0, 1, [
          {
            offset: 0,
            color: "rgba(0, 163, 255, 0.20)", // 0% 处的颜色
          },
          {
            offset: 1,
            color: "rgba(0, 163, 255, 0)", // 100% 处的颜色
          },
        ]), //背景渐变色
      },
    },
    lineStyle: {
      // 系列级个性化折线样式
      width: 4,
      type: "solid",
      color: "#00A3FF",
    },
  },
]

效果如下：