A friction torque analysis model of seeker servo mechanism including thermal coupling deformation was established. The influence of changing environment temperature on geometry parameters and friction torque of angular contact bearing was mainly studied. Taking mirror-type seeker as an example, its friction torque was calculated and analyzed by using the proposed calculation model. Results show that the grease viscosity is the main cause for the dramatic rise of the friction torque with the decreasing of the temperature, while the thermal deformation has a small impact on it. Based on the electrical method, an experimental system for friction torque measurement was established. And a rapid temperature experiment chamber was used to simulate environment temperature. Theoretical calculation results and experimental results were compared and analyzed. Experiments prove that the results of friction torque experiment agree with the theoretical model calculation.