Abstract: Since the thermal deformation of optical elements in the ambient temperature affects the system performance greatly, the simulation and analysis for the thermal distortion of optical elements are carried out with FEA to support the design of optical elements. A simulation and analysis method for the thermal deformation is put forward. It was implemented in following steps: problem analysis, thermal deformation simulation based on Ansys and data analysis. Each step was discribed. Taking the key elements of an optical system as the research objects, the thermal deformation simulation was performed by the method, data analysis was implemented with Matlab software. The parallelism of the two reflection mirrors is 7.62412″ at 40℃ of ambient temperature and it is 8.56317″ at -10℃. The results are basically consistent with the tested ones, and the validity of the method is verified.