代码

tooltip: {
            trigger: 'axis',
            formatter: function (params) {
              var relVal = params[0].name
              for (var i = 0, l = params.length; i < l; i++) {
                relVal +=
                  '<br/>' +
                  params[i].marker +
                  params[i].seriesName +
                  ' : ' +
                  params[i].value +
                  '(亿m³)'
              }
              return relVal
            }
          },

效果图