The liquid crystal display is high light, the advantage thin in thickness. In order to reach the thickness thinly, the request good in degree of consistency, it is important to design a qualified mould group in a poor light. This text introduces how to utilize Trace Pro optics to imitate the software , imitating to the diffusion board of the mould group in a poor light of the liquid crystal display , analysis and designing mainly. To the sidelight type mould group in a poor light, go to type in a poor light mould group construct comparatively simple , main optics for reflect board , spread scene , cold cathode tube and arris lens component its directly. The main use of reflection board lying below the mould group among them , in order to collect and reflect the light that come from the light source, make it penetrate above to in a poor light mould group, in order to increase the luminance of screen. Spread slice and function , arris of lens and the arris lens like mere sidelight type in a poor light mould diffusion slice of group, make their even to take in order to raise the luminance of screen light scattering separately. When the mould group in a poor light is thinner and thinner in thickness, brightness its disparity can more and more heavy too, so optics design more and more challenging. This text designs mainly to spread the distribution that the board adds the particle son to with the high degree of consistency, is it probe into in a poor light mould light neat degree that group can appear to come. Design a series of and reply the mould group which reflect the array, software Trace Pro is enabled being used for designing and replying the geometry structure which reflects the array and shut in the simulation optics route , analog quantity examines the result designed, and discuss its characteristic.