Abstract: A new double-gap vircator for high power microwave generation is proposed and studied by simulation in this paper. In the vircator, the interaction cavity is a cylindrical cavity separated into two resonators by a metal foil with a hole in the center. The vircator makes use of the side-extraction and coaxial output method. The quality factors of the cavity Ⅰ and Ⅱ are 6 960 and 71.8 respectively, the resonant frequency is 2.3 GHz. For an annular electron beam of 515 kV and 10 kA, by optimizing and using partial foil structures, the rms efficiency can reach 11% at an average output power of 570 MW at 2.4 GHz. Simulations show that the optimal impedance of the beam is about 51.5 W and the output efficiency increases with the increasing of beam current and keeps larger than 10% with the bea