void Start () {
        BG = GameObject.Find("BackGround");
        UIBG = BG.GetComponent<RectTransform>();
        ZeroScreen = new Vector3(Screen.width / 2, Screen.height / 2, 0);
    }

void Update () {
        //Debug.Log("UI" + UIBG.localPosition);
        //Debug.Log("Zero : "+ZeroScreen);
        MousePos = Input.mousePosition
 
;
        //Debug.Log("MousePos :　" + MousePos);
        Vector3 DetaMouse = MousePos - ZeroScreen;
        BG.GetComponent<RectTransform>().localPosition = -1 * DetaMouse * rate;
    }

原理很簡單，就是滑鼠到螢幕中心的位置，就是UGUI的位置的映象
再把Vector乘個Rate 感覺效果就出來了