The invention provides a light guide plate comprising a light guide plate body and a metal grating layer which is arranged at the upper surface of the light guide plate body. The metal grating layer is used for converting oblique light emitted by the light guide plate body into light which is vertical to the light guide plate body surface and radiates in side direction. The invention also provides a method for manufacturing the light guide plate. The method comprises following steps: holographic calculation and hologram manufacture; a metal grating layer formation at one side surface of the light guide plate body. The invention also provides a backlight module comprising a reflector plate, a light source, a lampshade, and the light guide plate, wherein at least one of the left side and the right side of the light guide plate is provided with the light source, the lampshade is arranged at the outer side in a covering mode, away from the light guide plate, of the light source, and the reflector is arranged under the light guide plate. According to the backlight module of the invention, through the installation of the metal grating layer, prismatic lens and diffusion sheets are saved so that the overall thickness of the backlight module is obviously reduced, and at the same time, the transmittance is increased, the viewing angle brightness is improved and the image quality is increased.