has found the problem. Yesterday, I looked up the relevant information on the Internet and found a solution. I asked and answered myself here, hoping to help friends in need:

1. Get all data series through option.series

2. Use callback in the formatter property of tooltip (which controls the properties of the suspension box) to return the character format to be displayed

3. Traverse series and series.data, in callback to assemble strings by judging whether the current data belongs to the current region

here is the code for the solution:

var chart = echarts.init(document.getElementById('mapChart'));
var countyInfo;
$.get('../../distributedHome/getHomeData.action',function(data){
    setChart();
});
function setChart(){
    $.get('data/hangzhou.json', function (hangzhoujson) {        //json
        echarts.registerMap('hangzhou', hangzhoujson);    //
        var option={
             title: {
                 text: '',
                 subtext: '',
                 textStyle:{
                     color:'-sharpfff'
                 }
             },
            legend:{
                 orient: 'vertical',
                 left: 'left',
                 data:['1','2']
            },
            tooltip: {        //
                trigger: 'item',
                formatter:function(params){
                    //res,
                    var res=params.name+'<br />';
                    //series
                    var myseries=option.series;
                    //series
                    for(var i=0;i<myseries.length;iPP){
                        //series[i],data:params.nameres
                        for(var k=0;k<myseries[i].data.length;kPP){
                            //console.log(myseries[i].data[k].name);
                            //dataname
                            if(myseries[i].data[k].name==params.name){
                                //seriesnameres
                                res+=myseries[i].name+':'+myseries[i].data[k].value+'<br />';
                            }
                        }
                    }
                    //res
                    //console.log(res);
                    return res;                
                },
                
                    
            },
            visualMap: {            
                min: 0,
                max: 1000,
                text:['High','Low'],
                realtime: true,
                calculable: true,
                inRange: {
                    color: ['lightskyblue','yellow', 'orangered']
                },
                textStyle:{
                    color:'-sharpfff'
                }
            },
            series: [{
                name:'1',
                type: 'map',    //
                map: 'hangzhou',    //
                aspectScale:1,    //
                roam: true,     // 'scale'  'move' true 
                layoutCenter:['50%','50%'],        //['50%','50%']
                layoutSize: '100%',        //100%
                label: {
                    normal: {
                        show: true    //
                    },
                    emphasis: {
                        show: true    //
                    }
                },
                data:[{    name:'',value:337},
                      {    name:'',value:37},
                      {    name:'',value:737},
                      {    name:'',value:237},
                      {    name:'',value:97},
                      {    name:'',value:137},
                      {    name:'',value:257},
                      {    name:'',value:217},
                      {    name:'',value:17},
                      {    name:'',value:837},
                      {    name:'',value:437},
                      {    name:'',value:77},
                      {    name:'',value:7}]
            },{
                name:'2',
                type: 'map',    //
                map: 'hangzhou',    //
                aspectScale:1,    //
                roam: true,     // 'scale'  'move' true 
                layoutCenter:['50%','50%'],        //['50%','50%']
                layoutSize: '100%',        //100%
                label: {
                    normal: {
                        show: true    //
                    },
                    emphasis: {
                        show: true    //
                    }
                },
                data:[{    name:'',value:127},
                      {    name:'',value:327},
                      {    name:'',value:521},
                      {    name:'',value:27},
                      {    name:'',value:167},
                      {    name:'',value:197},
                      {    name:'',value:417},
                      {    name:'',value:207},
                      {    name:'',value:117},
                      {    name:'',value:37},
                      {    name:'',value:757},
                      {    name:'',value:27},
                      {    name:'',value:71}]
            },{
                name:'3',
                type: 'map',    //
                map: 'hangzhou',    //
                aspectScale:1,    //
                roam: true,     // 'scale'  'move' true 
                layoutCenter:['50%','50%'],        //['50%','50%']
                layoutSize: '100%',        //100%
                label: {
                    normal: {
                        show: true    //
                    },
                    emphasis: {
                        show: true    //
                    }
                },
                data:[{    name:'',value:127},
                      {    name:'',value:327},
                      {    name:'',value:521},
                      {    name:'',value:27},
                      {    name:'',value:167},
                      {    name:'',value:197},
                      {    name:'',value:417},
                      {    name:'',value:207},
                      {    name:'',value:117},
                      {    name:'',value:37},
                      {    name:'',value:757},
                      {    name:'',value:27},
                      {    name:'',value:71}]
            }]
        }
        chart.setOption(option);
    });
    window.onresize=function(){
        chart.resize();
    }
}

solves the problem, but several for loops look dazzling.
the embarrassing thing is that the tooltip callback parameter param in echart2 contains the data of each set in series, while echarts3 only contains the data and data sum of the first set. Obviously it was written by a bug, programmer.