是我傻了，从官方另一个demo抄来的。
import { _decorator, CameraComponent, Component, Node, Vec3 } from ‘cc’;
const { ccclass, property } = _decorator;
@ccclass('Test')
export class Test extends Component {
@property(Node)
pos_3d: Node = null!;
@property(Node)
pos_2d: Node = null!;
@property(CameraComponent)
camera: CameraComponent = null!;
start() {
}
update(deltaTime: number) {
}
protected lateUpdate(dt: number): void {
let _v3_0: Vec3 = new Vec3(0, 0, 0);
this.pos_3d.getWorldPosition(_v3_0);
this.camera.convertToUINode(_v3_0, this.pos_2d.parent!, _v3_0);
this.pos_2d.setPosition(_v3_0)
}
}