Abstract: In this paper,the space-charge limiting current of coaxial drift tube is derived by the Green's function method. TWo-dimensional features of coaxial vircator is analyzed within the framework of steady-state relativistic-fluid Maxwell equations. The radial current arsing at the anode, and plasma frequency for electron beam can be abtained. The resulting plasma frequency solution agrees with the PIC simulation frequency. MAGIC, a 2(1/2)dimensional particle-in-cell codes are used to simulate the coaxial vircatot The output power, the FFT of output power and the plot of single frequency spectrum, and the time history of current are presented. GW output power is generated with 0.6 MV voltege, and microwave radiation efficiency is about 14.30%.