Abstract: Based on the advantages of the relativistic backward wave oscillator (RBWO) with low magnetic field and vircator, a novel configuration of vircator with a high beam-wave conversion efficiency is presented and the 2.5-D particle-in-cell simulations are carried out using a PIC code. When the energy of the electron is 480 keV while the beam current is 23 kA, a simulated result of 2.6 GW output microwave power with a frequency of 3.7 GHz is obtained, for which the beam-wave conversion efficiency of the vircator is 23%.