废话不多说，上代码 

需要将原来的 new echarts.graphic.LinearGradient   改成这样:

new this.$echarts.graphic.LinearGradient  that.$echarts.graphic.LinearGradient

//抄作业的渐变代码
itemStyle: {
        color: new echarts.graphic.LinearGradient(0, 0, 0, 1, [
           { offset: 0, color: "#6DF1FD" },
           { offset: 1, color: "#62D5FA" },
         ]),
        },



//vue中出问题的代码
itemStyle: {
        color: that.$echarts.graphic.LinearGradient(0, 0, 0, 1, [
           { offset: 0, color: "#6DF1FD" },
           { offset: 1, color: "#62D5FA" },
         ]),
        },



//解决后的Vue代码
itemStyle: {
        color:  new that.$echarts.graphic.LinearGradient(0, 0, 0, 1, [
           { offset: 0, color: "#6DF1FD" },
           { offset: 1, color: "#62D5FA" },
         ]),
        },