A coaxial Bragg reflector with tapered inner rode corrugated ripples and phase matching section used in relativistic diffraction generator (RDG) with overmode cylindrical structure in Ka-band is presented and analyzed in this paper. The conservation of complex power technique(CCPT) is introduced to analyze the frequency response of the Bragg reflector. The influences of the phase matching section length, the corrugated sinusoidal slots depth and the tapered angle of the reflector on frequency response are studied. It is found by analyzing the influence of the initial ripple phase that the reflector has a favourable characteristic for mode selection. The research results provide important theoretical analysis and data reference for designing coaxial Bragg reflector structure.