In order to realize the lightness of the LCD(liquid crystal display)and further reduce the thinness and the cost of backlight module, composite optical films have become the focus of research and development of most optical films manufacturers. In this paper, the structure of the backlight module and the optical performance of the optical film for liquid crystal display are described and optical efficiency of optical films for LCD are described. The pivotal factors in the process of optical films recombination are studied by using light tools software. The influenced mechanism of prism angle, prism pitch and prism peak penetration depth (D) are evaluated. Two types of composite optical films structure are separately discussed and simulated, one is two-in-one structure; another one is three-in-one structure include. Through using the light tools simulation, the optical effects are evaluated and analyzed from the point of view of center brightness, uniformity and visual angle. Via the phenomenon of stimulating, the improvement characteristics of optical composite structure with two different combination structures for display picture are obtained. Through simulation and experiment, it is found that when the top angle of prism is 90°, the pitch of prism is from 24 μm to 54 μm, and the penetration depth (D) is 1～3 μm, the brightness uniformity of composite optical diaphragm can reach more than 81%. This research has certain guiding significance for practical application and development about composite optical films, which will help to speed up the development progress of backlight module and reduce the thickness and cost of backlight module.