Abstract: The dispersion characteristics of corrugated waveguide with an inner coaxial structure are studied and the influences on dispersion characteristics of the corrugation period, amplitude and the radius of the inner coaxial conductor are discussed. It is shown that the cutoff frequency of system increases with the introduction of inner coaxial conductor, the size of system can be greater than conventional corrugated waveguide BWO, large radius hollow electron beam could be used and device could operate with a low guiding magnetic field. A PIC simulation is carried out using MAGIC software, which shows that the field distribution of coaxial waveguide is beneficial to the beamwave interaction. A nonuniform coaxial BWO with high interaction efficiency of 60% and low guiding magnetic field l