Based on physic-optics and geometric-optics, a design method of high power microwave feed vacuum output window was discussed. For an X band, 1.5 GW pulse power handling ability gaussian feed, a dishing type of Teflon vacuum output window was fabricated, with a diameter of 548 mm, a height of 83.4 mm and a thickness of 33.4 mm. The test results are in good agreement with theoretics. The voltage standing wave ratio(VSWR) at the central frequency 9.3 GHz was 1.07. The band with VWSR less than 1.24 was 9%. The direction pattern of the feed with the dielectric window was the same as that without the dielectric window. The temperature distribution was analysed by one dimension stable heat transmission theory.