Abstract: The present invention provides a resembling prismatic structure of light guide plate to economize the optical films such as prismatic film, diffusion film, reflection film and . . . etc. The present invention simplifies the multifarious structures of the prior LCD backlight modules. It can efficiently decrease the material of making the backlight module and the cost of the manufacturing time. In comparison with that conventional LCD backlight module emits light wholly, continuously and evenly from light emitting face of light guiding plate. Large amount of energy is wasted in the conventional backlight module owing to its illumination on the opaque part of LCD substrate such as common electrode and black matrix.