The beam-wave interaction efficiency of a 170GHz megawatt-level corrugated coaxial-gyrotron operating with TE_(31,12) mode was studied numerically. According to the self-consistent nonlinear theory, the efficiencies of two types of coaxial resonator were calculated and compared. Taking into account electronic velocity spread and cavity wall resistivity, the beam-wave interactions of improved cavity were investigated. The relationships between efficiency and magnetic field, voltage, current, beam radius, velocity ratio, and parameters of groove are presented. The results show that the voltage and magnetic field have great influence on efficiency, but the current and velocity spread do slightly. The optimized geometry parameters can improve efficiency, reduce the impact of velocity spread on efficiency, and achieve around 48.6% electronic efficiency and 1.7MW output power at 5% velocity spread and 6.896×10~(-8) Ωm resistivity. The beam-wave interaction efficiency of a 170GHz megawatt-level corrugated coaxial-gyrotron operating with TE - (31,12) mode was studied numerically. According to the self-consistent nonlinear theory, the efficiencies of two types of coaxial couple were calculated and compared Taking into account electronic velocity spread and cavity wall resistivity, the beam-wave interactions of improved cavity were investigated. The relationships between efficiency and magnetic field, voltage, current, beam radius, velocity ratio, and parameters of groove are presented. show that the voltage and magnetic field have great influence on efficiency, but the current and velocity spread do slightly. The optimized geometry parameters can improve efficiency, reduce the impact of velocity spread on efficiency, and achieve around 48.6% electronic efficiency and 1.7MW output power at 5% velocity spread and 6.896 × 10 -8 Ωm resistivity.