Abstract: ZLL medium membranoe reflector, the wide of its firing area is determined by the size of reflectors' quadric and curvature and by its arrangement of small ladder-shaped surfaces. In this article, we adopt computer analogue method, making illuminant pass to the reflect surface, then from the reflect surface to the light-sensitive surface. The beam passing quantity may reach maxinum, we can adjust cur curvature, angle of incidence and the position of illuminant to get the designed satisfactory lighting condition.