The radiation fields and the design of coaxial biconical antenna are obtained with the field of equivalent Huggens source on the spherical surface aperture. The experiment of high power coaxial biconical antenna which has been operated in ultrawide band pulse of high voltage　±100kV, high repetition rate 100Hz, pulse duration 3.6ns, and the radiation peak power more than 100MW are also presented. The antenna band wide is from 15MHz to 1GHz，input impedance 50Ω; The FWHM of an tenna patterns for peak power in E plane and H plane is 50°　and 360°, respectively, radiation efficiency more than 65%.