int layer =  << ;

Ray myray = UICamera.currentCamera.ScreenPointToRay(Input.mousePosition);

RaycastHit[] hits = Physics.RaycastAll(myray, 1000.0f, layer);

int layer =  << ;//NGUI layer, TODO modify with your own

void Update()

{

    if (Input.GetMouseButtonUp())

    {

        //UICamera

        if (UICamera.currentCamera != null)

        {

            Ray myray = UICamera.currentCamera.ScreenPointToRay(Input.mousePosition);

            RaycastHit[] hits = Physics.RaycastAll(myray, 1000.0f, layer);

            if(hits != null && hits.Length > ){//hit the NGUI layer

                return;

            }

        }
　　　　

    }

}