Abstract: The thermal deformation of silicone on glass (SOG) Fresnel lens made up of silicone and glass can affect the performance of concentrating photovoltaic (CPV) system. In order to investigate the influence, we designed and optimized two kinds of CPV concentrator systems. Then, we calculated the thermal deformation of Fresnel lens with finite element analysis method, as well as the concentration efficiency of the system through Monte Carlo method. The calculation indicates for the single stage concentrator system, the Fresnel lens designed with monochromatic light uniformity method is obviously affected by the warpage deformation of concentrator and free deformation of prisms. The difference of optical efficiency is about 10% between the deformed and the undeformed concentrator system. However, the Fresnel lens designed with improved method that compensates for dispersion is little influenced by thermal deformation. Moreover, the twostage concentrator system can be greatly resisted to the thermal deformation.