In order to improve the optical performance of optical window,the influences of aerodynamic and atmospheric environment on optical window are analyzed.Based on the theory of aerodynamics,the Mach number and Reynolds number are calculated.The convection heat transfer coefficient on outer surface of optical window glass is calculated by the theory of longitudinally sweeping plan mural,the temperature distribution is simulated,and the influence of axial temperature difference on wave front error of optical window is analyzed.Based on several physical characteristics,the reason and result of defrost are discussed,and the solution which prevents defrost is put forward.The flight test result shows that the analysis conclusion is correct and the solution is appropriate.The study provides valuable reference for the optical window design.