Abstract: In a backlight system of a liquid crystal display, a light guide plate includes a plurality of reflector units. The light guide plate is in wedge or flat shape, which has a front surface, a back surface, and four side surfaces. The plurality of reflector units are integrally formed with the back surface of the light guide plate, each of which is designed as an annular protrusion. Through one of the four side surfaces, a light beam irradiated by a lamp propagates into the light guide plate. Regardless of the propagating direction, part of the light beam is reflected by the reflector unit into two reflective light beams that are then refracted out of the front surface of the light guide plate. Therefore, the light guide plate according to the present invention achieves an excellent reflective efficiency.