Ohmic losses of a coaxial cavity gyrotron with outer corrugation are investigated.The results show that the averaged ohmic loss densities of the inner and outer conductors have similar changes along with the axial direction of the gyrotron;whereas averaged ohmic loss densities of the outer conductor are more than the inner conductor;the outer slot depth and width cause greatly the averaged ohmic loss densities of the corrugation bottom and the corrugation period of outer conductor,and averaged densities of ohmic losses on the inner conductor are almost unaffected.