原来的效果

修改后实现效果

解决- 需要修改elementui的依赖包中lib/element-ui.common.js中的源码
将js中此处代码改完下面的代码

watch: {
        // don't trigger getter of currentRow in getCellClass. see https://jsfiddle.net/oe2b4hqt/
        // update DOM manually. see https://github.com/ElemeFE/element/pull/13954/files#diff-9b450c00d0a9dec0ffad5a3176972e40
        // 修改 包含子集的树形数据的table 中 移入子集背景色问题  _this3.$parent.$parent.$parent.$el -和页面元素有关 如果包了很多层div的话 要精准寻找
        'store.states.hoverRow': function storeStatesHoverRow(newVal, oldVal) {
          var _this3 = this;
          let expandedRow = _this3.$parent.$parent.$parent.$el.querySelectorAll('.expanded')
          if (expandedRow.length) {
            if (this.$isServer) return;
            // 如果dom元素包含类名expanded 说明有子集
            var raf = window.requestAnimationFrame;
            if (!raf) {
              raf = function raf(fn) {
                return setTimeout(fn, 16);
              };
            }
            raf(function () {
              // 查找到子集中同时包含.el-table__body-wrapper(左边tr所在的dom) .el-table__fixed-right(右边定位table所在的dom) 然后获取这两个dom中的所有的.el-table__row (只要表格使用了固定 则会有两套dom显示 所以要获取两套dom中移入触发的tr)
              var rows1 = _this3.$parent.$parent.$parent.$el.querySelectorAll('.el-table__body-wrapper .childrenTable .el-table__row');
              var rows2 = _this3.$parent.$parent.$parent.$el.querySelectorAll('.el-table__fixed-right .childrenTable .el-table__row');
              if (rows1) {
                var oldRow = rows1[oldVal];
                var newRow = rows1[newVal];
                if (oldRow) {
                  Object(dom_["removeClass"])(oldRow, 'hover-row');
                }
                if (newRow) {
                  Object(dom_["addClass"])(newRow, 'hover-row');
                }
              }
              if (rows2) {
                var oldRow = rows2[oldVal];
                var newRow = rows2[newVal];
                if (oldRow) {
                  Object(dom_["removeClass"])(oldRow, 'hover-row');
                }
                if (newRow) {
                  Object(dom_["addClass"])(newRow, 'hover-row');
                }
              }
              
            });
          } else {
            // this.store.states.isComplex 父级table是否包含固定列
            if (!this.store.states.isComplex || this.$isServer) return;
            var raf = window.requestAnimationFrame;
            if (!raf) {
              raf = function raf(fn) {
                return setTimeout(fn, 16);
              };
            }
            raf(function () {
              var rows = _this3.$el.querySelectorAll('.el-table__row');
              var oldRow = rows[oldVal];
              var newRow = rows[newVal];
              if (oldRow) {
                Object(dom_["removeClass"])(oldRow, 'hover-row');
              }
              if (newRow) {
                Object(dom_["addClass"])(newRow, 'hover-row');
              }
            });
          }
        },
      },