Abstract: In order to reduce the influence of large aperture optical window on the system's incident light and strengthen the performance of optical window and the imaging quality of the optical system, an intermediate zonal auxiliary supporting form (IZASF) based on the ordinary zonal supporting form (OZSF) is proposed in this paper. The influence of these two supporting forms on the wavefront error of optical system was compared under different caliber, thickness ratio and obscuration ratio. Compared with the ordinary zonal supporting form, the intermediate zonal auxiliary supporting form can reduce the wavefront error of the window by 90%. The wavefront error of this window with diameter-thickness ratio 100∶1 and the supporting form IZASF is similar to that of the window with diameter-thickness ratio 100∶3 and the supporting form OZSF. Therefore, the IZASF can effectively improve the supporting efficiency of window and reduce the window thickness and quality. It can also reduce absorbance of the incident light, thus it has great significance to improve the performance and expand the application environment of optical telescopes further.