Abstract: In some severe application environment of reflector antenna, temperature difference is very large. Reflector antenna may appear structural stress and deformation due to the different thermal expansion coefficients of its various composite materials. This deformation will bring bad effects on antenna electric properties. For the coupling problem between thermal deformation and electromagnetic field, this paper establishes the method for analyzing the effects of thermal deformation on far-field pattern. Firstly, mechanical model is established by Patran to get the thermal deformation field of the model under 100 ℃ temperature difference using Nastran. Then, the deformed mesh model is input into FEKO, the effect of thermal deformation on the far-field pattern is analyzed quantitatively. By controlling the mesh model, the mechanical model and electromagnetic model use the same mesh model, so as to reduce the artificial error of mesh transform. This research provides quantitative theoretical foundation for the converse design of reflector antenna.