Based on the thermal-optical analysis, the glass thickness of the corrector mirror used as an optical window is optimized under the complex environment. The intensity and the thermal environment of the corrector mirror is analyzed. By mapping the temperature field to structural model, the deformation and surface data of the corrector mirror under the thermal-force coupling condition are calculated by the finite element method. The surface data of corrector mirror is fitted and calculated. Finally, the processed surface data of corrector mirror is brought into the optical design scheme, and the effect of the thickness of corrector mirror on the performance of spectrometer is analyzed. The results show that the thickness of the corrector mirror should be no less than 10 mm. If the thickness of the corrector mirror is 15 mm, the effect of thermodynamics on corrector mirror can be ignored. It is conclused that the corrector mirror acting as optical window can not only meet the strength and reliability requirements, but also meet the optic index of the spectrometer. These results provide the guidance for the optical window design.