Recently, CAE modlex 3D software is used to analyze mole injection and design. It is efficient to simulate both characteristics of stress and heat transfer in mold injection. In order to get better heat transfer effect on mold injection, it can be improved in mold design. In this paper, the theory of field synergy principle is put into use and change parameters in mold injection. The results show that field synergy principle is sufficient to improve light guide plate efficiency and geometry of mold injection.