Abstract: In order to have the high-power microwave(HPM) source of the three-unit transit-time tube oscillator(TTTO) has the character of unidirectional beam and line polarization, a circular waveguide bevel cut radiation antenna is designed. Experimental research is the emphatic part. Experiment condition as well as factors that should be considered during the design is presented. The length of the coaxial inner-conductor has been regulated, and the form of the nose taper has been choosed, which belong to the modes convertor in the front of the circular waveguide. Then, the better result s are finally presented. The reliability and practicality of this antenna have been proved.