CaF\-2 was chosen as the window material. The experiment was guided to test the influence of the window on beam quality while the window was at high temperature and stress. A deterioration of high energy laser beam quality caused by temperature rise and deformation of CaF2 window was presented in our experiment. After the far-field beam spot of high energy laser is analyzed, and the far-field beam spot's radius increase rapidly owing to the heating effect of CaF₂ window is shown. Therefore, the influence of heating effect of CaF₂ window on beam quality is verified.