Abstract: In order to further improve and optimize the topological structure of the high-power radial line array antenna, increase the power capacity, and satisfy the demand of the vacuum sealing of feed source, a microwave output window suitable for high-power radial line array antenna was designed. The material of the high-power radial line output window is circular ceramic, whose permittivity is 9.4, the thickness of the window is 3 mm, and inner radius of the window is 36 mm. It can realize vacuum sealing of the radial line array antenna feed system between the input coaxial waveguide and the output coaxial waveguide. Under the center frequency of 2.856 GHz, this radial line output windows standing-wave ratio is 1.03, insertion loss is 0.17 dB and power capacity attain about 150 MW.