Based on the fracture mechanics analysis, the glass thickness of the optical window of an airborne multi-spectral camera is designed in detail. Correlation analyses solve the engineering design problems of the optical window thickness and ensure the design more reasonable and reliable. Considering the complex environment, steady-state temperature field is calculated by means of finite element method. Linking temperature load to generalized force load, the deformation of optical window under the structure-thermal coupling condition is calculated. Optical window surface after deformation are derived by fitting the final deformation value using Zernike polynomial fitting. Fitting coefficients as the input of Zemax, the impact of the deformation of the optical window on the optical performance of multi-spectral camera is analyzed by means of wavefront error and modulaiton transfer function (MTF) as a measurement of imaging quality. The result shows that based on the known operational environment, the impact on imaging quality of optical system is negligible.