Abstract: The finite element method was used to study the deformation distribution of the optical window of the multi-component gas in-situ laser detection system under different thermal pressing loads, and the refractive index distribution of the optical window was calculated according to the thermo-optic effect. The influence laws of the refractive index change and deformation of the optical window before and after nitrogen purging on the luminous flux and irradiance distribution reaching the receiving surface were compared and analyzed by ray tracing method. In addition, based on the laser transmission test platform of high-temperature optical window, the influence of high-temperature optical window on the detection signal was studied. The results show that the high-temperature and high-pressure environment will increase the refractive index change amplitude and deformation of the optical window, which resulting in the laser optical path deflection induced transmitted light intensity loss and probe signal fringe interference. The nitrogen purging can effectively improve the laser transmission conditions, increase the luminous flux reaching the receiving surface, optimize the irradiation distribution and improve the laser transmission quality.