官网文档

element-ui官网文档有默认展开和默认选中

<el-tree
  :data="data"
  show-checkbox
  node-key="id"
  :default-expanded-keys="[2, 3]"
  :default-checked-keys="[5]"
  :props="defaultProps">
</el-tree>

<script>
  export default {
    data() {
      return {
        data: [{
          id: 1,
          label: '一级 1',
          children: [{
            id: 4,
            label: '二级 1-1',
            children: [{
              id: 9,
              label: '三级 1-1-1'
            }, {
              id: 10,
              label: '三级 1-1-2'
            }]
          }]
        }, {
          id: 2,
          label: '一级 2',
          children: [{
            id: 5,
            label: '二级 2-1'
          }, {
            id: 6,
            label: '二级 2-2'
          }]
        }, {
          id: 3,
          label: '一级 3',
          children: [{
            id: 7,
            label: '二级 3-1'
          }, {
            id: 8,
            label: '二级 3-2'
          }]
        }],
        defaultProps: {
          children: 'children',
          label: 'label'
        }
      };
    }
  };
</script>

可以看出  :default-checked-keys="[5]"绑定的是一个数组，元素是每个勾选框的id

html：

<el-tree
        ref="tree"
        :data="memberList"
        show-checkbox
        default-expand-all
        node-key="id"
        highlight-current
        :props="defaultProps"
        :filter-node-method="filterNode"
></el-tree>

memberList数据样式为（可以看出根节点多了个teamFlag）：

[
    {
        "id": "F92FE4F9C6F95E18E055000000000001",
        "userName": "A班组",
        "memberList": [
            {
                "id": "F92FE4F9C6FA5E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "0fbd222725c748299fdc178987569d4b",
                "userName": "小阮",
                "teamType": null
            },
            {
                "id": "F92FE4F9C6FB5E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "9d16ac4119064bbe865102494137a3c8",
                "userName": "tw2t",
                "teamType": null
            },
            {
                "id": "F92FE4F9C6FC5E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "d55760ebd5c04f2c869ab084be6f4e6b",
                "userName": "tw2leader",
                "teamType": null
            },
            {
                "id": "F92FE4F9C6FD5E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "cdf0c8dcf93f4dfc8602ff59e0b8d191",
                "userName": "tw3t",
                "teamType": null
            },
            {
                "id": "F92FE4F9C6FE5E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "885d106031784e6caa2f9fcfb3feab32",
                "userName": "TWTWO",
                "teamType": null
            },
            {
                "id": "F92FE4F9C6FF5E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "eb0533610a48411aa6124484aef107a1",
                "userName": "tw2",
                "teamType": null
            },
            {
                "id": "F92FE4F9C7005E18E055000000000001",
                "teamId": "F92FE4F9C6F95E18E055000000000001",
                "userId": "0998d44318fa44f3bb033030adcea1d4",
                "userName": "rh",
                "teamType": null
            }
        ],
        "teamFlag": "team"
    },
    {
        "id": "F92FE5D8EB055E14E055000000000001",
        "userName": "B班组",
        "memberList": [
            {
                "id": "F92FE5D8EB065E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "9eb123238f464b5f9ce2b55d98a7151f",
                "userName": "tw3",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB075E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "a687747a84b541b9a5dadb6cedbaac60",
                "userName": "tw3s",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB085E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "7ed742cf308a4e6e876d19c85ab87bc5",
                "userName": "tw2s",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB095E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "1c4745174b2443bcb0f692b4206dd565",
                "userName": "陈爱国",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB0A5E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "37a3167e7bf34e7794080cf3580206ea",
                "userName": "tw1",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB0B5E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "fbbbf36302d444be8a6b3e01cbc761c4",
                "userName": "tw4s",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB0C5E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "16d7b52ec5c24bde8b0db1ea76f3c2d1",
                "userName": "tw4t",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB0D5E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "add97170833e4321a90440f9a80ff650",
                "userName": "tw4",
                "teamType": null
            },
            {
                "id": "F92FE5D8EB0E5E14E055000000000001",
                "teamId": "F92FE5D8EB055E14E055000000000001",
                "userId": "584f437636f04ffca8cce346a80c4b17",
                "userName": "tw1leader",
                "teamType": null
            }
        ],
        "teamFlag": "team"
    },
    {
        "id": "F92FE5D8EB0F5E14E055000000000001",
        "userName": "C班组",
        "memberList": [],
        "teamFlag": "team"
    },
    {
        "id": "0B2EE330883E04CCE065000000000001",
        "userName": "D班组",
        "memberList": [
            {
                "id": "0B2EE330883F04CCE065000000000001",
                "teamId": "0B2EE330883E04CCE065000000000001",
                "userId": "52d863f6232f45cf9abbdb483e9349ac",
                "userName": "塔台讲评室",
                "teamType": null
            },
            {
                "id": "0B2EE330884004CCE065000000000001",
                "teamId": "0B2EE330883E04CCE065000000000001",
                "userId": "d35a2f81166b47c5aad011a665863b2a",
                "userName": "塔台",
                "teamType": null
            },
            {
                "id": "0B2EE330884104CCE065000000000001",
                "teamId": "0B2EE330883E04CCE065000000000001",
                "userId": "6f349b9acd0a431ab77797afdc987202",
                "userName": "TWONE",
                "teamType": null
            }
        ],
        "teamFlag": "team"
    }
]

第一次勾选完生成this.checkedMemberList发送给父数组：

this.checkedMemberList数据（把有teamFlag的删除了，就是删除了根节点其实可以不删）：

[
    {
        "id": "F92FE4F9C6FA5E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "0fbd222725c748299fdc178987569d4b",
        "userName": "小阮",
        "teamType": null
    },
    {
        "id": "F92FE4F9C6FB5E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "9d16ac4119064bbe865102494137a3c8",
        "userName": "tw2t",
        "teamType": null
    },
    {
        "id": "F92FE4F9C6FC5E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "d55760ebd5c04f2c869ab084be6f4e6b",
        "userName": "tw2leader",
        "teamType": null
    },
    {
        "id": "F92FE4F9C6FD5E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "cdf0c8dcf93f4dfc8602ff59e0b8d191",
        "userName": "tw3t",
        "teamType": null
    },
    {
        "id": "F92FE4F9C6FE5E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "885d106031784e6caa2f9fcfb3feab32",
        "userName": "TWTWO",
        "teamType": null
    },
    {
        "id": "F92FE4F9C6FF5E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "eb0533610a48411aa6124484aef107a1",
        "userName": "tw2",
        "teamType": null
    },
    {
        "id": "F92FE4F9C7005E18E055000000000001",
        "teamId": "F92FE4F9C6F95E18E055000000000001",
        "userId": "0998d44318fa44f3bb033030adcea1d4",
        "userName": "rh",
        "teamType": null
    }
]

在父组件中处理子组件传过去的选择的元素（主要是this.form.selectedMembe）：

    //选择参加人员窗口关闭时
    handleMemberDialog(flag, memberList) {
      this.selectMemberVisible = flag;
      this.form.selectedMember = memberList;
      this.form.memberName = memberList
        .map((item) => {
          return item.userName;
        })
        .join(",");
      let arrList = this.form.memberName.split(",");
      this.$set(this.form, "checkboxGroup", arrList);
    },

父组件中对子组件的传递：

子组件处理父组件传递过来的数据（就是获取selectedMember数组的元素的id就够了）

openInit() {
      if (this.selectedMember && this.selectedMember.length > 0) {
        this.$refs.tree.setCheckedKeys(
          this.selectedMember.map((item) => {
            return item.id;
          })
        );
      } else {
        this.$refs.tree.setCheckedKeys([]);
      }
    },

          this.selectedMember.map((item) => return item.id })

[
    "F92FE4F9C6FA5E18E055000000000001",
    "F92FE4F9C6FB5E18E055000000000001",
    "F92FE4F9C6FC5E18E055000000000001",
    "F92FE4F9C6FD5E18E055000000000001",
    "F92FE4F9C6FE5E18E055000000000001",
    "F92FE4F9C6FF5E18E055000000000001",
    "F92FE4F9C7005E18E055000000000001"
]