.my-table table {
 width: 100% !important;
}

.my-table {
 width: calc(100% - 100px);
}

columns: [{
 title: '标题',
 width: 200 // 不加这东西
}]

<Col span="8"> 时 间：
 <Date-picker type="month" format="yyyy-MM" :clearable='false' :editable='false' :options="startOption" v-model="searchParams.sDate" style="width: 200px"></Date-picker>&emsp;至&emsp;
 <Date-picker type="month" format="yyyy-MM" :clearable='false' :editable='false' :options="endOption" v-model="searchParams.eDate" style="width: 200px"></Date-picker>
</Col>
<Table stripe :columns="tableColumns" :data="tableData"></Table>

// 初始化表头
  columsInit () {
   let timeStr1 = this.$utils.time.formatTime(this.searchParams.sDate, 'YYYY-MM')
   let startMonth = timeStr1 + '月维护企业数'
   let timeStr2 = this.$utils.time.formatAddTime(this.searchParams.sDate, 'YYYY-MM', 1, 'months')
   let midMonth = timeStr2 + '月维护企业数'
   let timeStr3 = this.$utils.time.formatTime(this.searchParams.eDate, 'YYYY-MM')
   let endMonth = timeStr3 + '月维护企业数'
   this.tableColumns.splice(3, 4,
    {
     title: startMonth,
     align: 'center',
     render: (h, params) => {
     //下面业务逻辑直接不用看
      // console.log(timeStr1)
     /*  let arr = params.row.historyDataListDto || [];
      let obj = null
      arr.forEach((item, index) => { //有些人员，有些月份的数据没有
       if (item.month == timeStr1) {
        obj = arr[index]
       }
      })
      if (obj) {
       return h('a', {
        on: {
         click: () => {
          this.toDetail(params.row.uId, params.row.class2Id, obj.month, obj.month, obj.dirId)
         }
        }
       }, obj.whsNum)
      } else {
       return h('span', '--')
      }
     */业务逻辑
     }
    },
    {
     title: midMonth,
     align: 'center',
     render: (h, params) => {
     
     }
    },
    {
     title: endMonth,
     align: 'center',
     render: (h, params) => {
      
     }
    },
    {
     title: '平均',
     align: 'center',
     key: 'avgNum'
    }
   )
  },