Abstract: A new structure of the coaxial vircator is proposed and studied numerically in this paper. Using the coaxial extraction structure, the beam-wave interaction and energy extraction are carried out separately. The left wall of the extraction cavity will reflect the microwave, thus provide a feedback for the beam-wave interaction; And it can also absorb the used electrons drifting in the outer space of the interaction region. When a pulse with peak voltage of 500kV is fed into the vircator, a peak instant power greater than 2.5GW is achieved by simulation at 2.175GHz; the peak period-averaged power reaches 1.2GW with an rms efficiency of 11%. The output power has high mode purity and narrow bandwidth as in a conventional coaxial viractor.