A prism sheet for a LCD backlight module is provided. The prism sheet contains a base layer and a prism layer formed on a side of the base layer. The prism layer contains multiple parallel latitudinal and longitudinal prism lenses intersecting with each other. As such, the prism sheet could provide both latitudinal and longitudinal convergence for the scattered lights from the diffusion film. Additionally, by adjusting the apex angles, shapes, and heights of the prism lenses, optimal horizontal and vertical viewing angles of the LCD display could be achieved.