Abstract: In the design of infrared optical system, the impact of thermal effect on optical performance should be taken into account so as to achieve a good temperature performance and the integrated opto-mechanical-thermal analysis should be conducted. The method and flow chart of integrated optomechanical-thermal analysis were discussed. An infrared lens with a focal length of 200 mm was designed, which matched with cold shield and could operate at a wide temperature range. The finite element model of the infrared lens was established and the thermodynamic analysis was accomplished, each lens interval and surface figure changes were obtained by using processed analysis data. The interval changes, Zernike coefficients and refractive index at ambient temperature were substituted into optical design software, and the temperature effect on image quality was obtained. The analysis results show that the modulation transfer functions of infrared lens with 16 line pairs in all field of views are larger than 0.5 from -40℃ to +60℃. The design of infrared lens is easy to be implemented and meets the requirements.