Aero-optical effect caused by infrared window in aerothermal environment has a serious effect on infrared imaging detector of high-speed missile. Experimental study on this effect which was carried through in plasma wind tunnel was represented in the paper. The surface temperature and heat flux of infrared window were measured in the experiment. Wavefront phase of light through the infrared window was measured with a radial shearing interferometer. The changes of point spread function and Strehl ratio with duration of heat were obtained. It is validated that infrared windows result in intensity attention and energy distribution disperse for light beam in far-field.