1. 设置默认选中：

使用 default-checked-keys 属性，设置默认要选中的节点，以数组形式，如下：

<el-treeref="treeRef":data="data"show-checkboxnode-key="id":props="defaultProps":default-checked-keys="[5]"
/>

2. 调用 Tree 实例对象的 getCheckedKeys 方法来获取选中的所有节点，如下：

const treeRef = ref();
const checkedId = ref([]);function getCheckedId() {checkedId.value = treeRef.value?.getCheckedKeys();
}

完整代码如下：

<template><div><el-treeref="treeRef":data="data"show-checkboxnode-key="id":props="defaultProps":default-checked-keys="[5]"/><el-button @click="getCheckedId">获取选中节点: {{ checkedId }}</el-button></div>
</template><script setup>
const defaultProps = {children: "children",label: "label",
};
const data = [{id: 1,label: "Level one 1",children: [{id: 2,label: "Level two 1-1",children: [{id: 3,label: "Level three 1-1-1",},{id: 4,label: "Level three 1-1-2",},],},],},{id: 5,label: "Level two 1",},
];
const treeRef = ref();
const checkedId = ref([]);function getCheckedId() {checkedId.value = treeRef.value?.getCheckedKeys();
}
</script>