Abstract: Coaxial vircator with feedback and beam modulation is designed and studied by theoretical and PIC simulation methods. In the vircator, there are a coaxial resonant cavity that beams pass through and a coupling gap connecting the coaxial resonant cavity and the drift tube, and beam can be modulated before microwave generated in the coaxial resonant cavity. Then the modulation can be strengthened by microwave from the drift tube to the coaxial resonant cavity through the coupling gap. Simulation results and theoretical analysis show that the coaxial vircator has high beam-wave transform efficiency and point frequency. Meanwhile, it is found that the frequency of the microwave that the vircator generates is locked by the coaxial resonant cavity, which can be tuned by tuning the parameters of