Abstract: Illumination system is an important part of the augmented reality (AR) optical system, and its volume, illumination uniformity and energy utilization directly affect the quality of the AR system, so it is important for secondary light distribution of light source in illumination system. The free-form surface lens and illumination system of the AR system were studied, and the correspondence between light collecting angle and volume of collimating system was analyzed. Based on the detailed analysis of surface shape construction of collimating system, the surface shape of catadioptric collimating system reflected by the central transmission edge was solved. Combined with partial differential equation method and meshing method, a free-form lens was designed. The liquid crystal on silicon (LCoS) illumination system was composed of system and polarized beam splitter prism. After simulation analysis, the system illumination uniformity is 91.96%, and the optical efficiency is 66.6% without the effect of polarization. The system has simple and compact structure, small volume, light weight, and high illumination uniformity, which can meet the needs of AR glasses.