Mathematical simulation of mold flow of glass fibers and design of heat transferring of plane mould for low pressure sheet molding compound were analyzed and optimized by MATLAB software in this article. The flexural properties of specimens molded in conventional and thermal-deign optimized mould were compared. The fracture surfaces of specimens were carefully investigated by SEM, too. The results show that the surface temperature of the mould was highly uniform during the process of curing when the distribution of the heating pipes in the plane mould was optimized. The flexural strengths of the specimens, cut from the center and the corner of the parts molded by thermal optimized mould, are almost the same and can reach about 170MPa. And the distribution of glass fiber with high weight content adhering well with resin is uniform in the fracture area.