Abstract: The Yunnan 1m Solar Telescope (YNST)is a vacuum telescope.It uses four flat vacuum windows to seal off the vacuum.The entire light transmitance will be reduced by the vacuum windows, and a part of the reflected light will change into the scattered or stray light.In this paper the influence of the vacuum window is analyzed.Based on the suggestion of the YNST Science Case Group, an optimum technique has been used to determine the layer thickness for a coating design.The coating will include minimal layers to maximize the energy throughput of the system on the key wave, and minimize the scattered or stray energy.In this way, the antireflection coating over a wide wavelength interval can easily be gotten, and the ratio of utilization of the optical energy can be increased.