Abstract-Design and optimization of high-power microwave (HPM) feed horn by combining the aperture field with radiation patterns are presented in the paper. The optimized feed horn in C band satisfies relatively uniform aperture field, power capacity higher than 3 GW, symmetric radiation patterns, low sidelobes, and compact length. Cold tests and HPM experiments were conducted to investigate the radiation patterns and power capacity of the horn. The theoretical radiation patterns are consistent with the cold test and HPM experimental results. The power capacity of the compact HPM horn has been demonstrated by HPM experiments to be higher than 3 GW.