Abstract: Radition field of plate-conical horn excited by circular waveguide TM01 mode is analysised by analytic formulations at first,Radition field and reflect coefficient are also calculated by using simulation software,theoretical analysis and experimental results show that the horn radiates linear polarized pattern with a boresight peak along the axis of the source,and geak gain of the horn is higher than 21dB,radiation efficiency is about 93~94% at 5GHz.