An analysis model about the effects of the temperature on the imaging and detection performance of the space infrared optical system was established. Firstly, on the basis of the finite element analysis, the optical surface deformation was characterized by Zernike polynomials. Considering the effect of temperature on materials' refractivity, the analytical method of MTF was improved, and then the changing rule of system MTF with the variation of thermodynamics and inertial load was presented. Secondly, the calculation model of camera background radiation was established by integrating the spontaneous radiation of the system, based on the heat transfer mechanics. This model can be used to calculate the irradiance generated by the spontaneous thermal radiation in image plane. Then the performance analysis method of infrared optical system was proposed. Finally, experiments were conducted using a real space infrared optical system. Experimental results indicate that when the system thermal control temperature is set at 10 ℃, the background radiation can be decreased by 48.6%, as MTF can be decreased by 30% as well. The proposed method can be used to study the background radiation of space infrared optical system and the changing rule of the system's imaging quality, and then optimize the system's working temperature, which provides theoretical guidance for thermal control design.