Abstract: The initial design of magnetron injection gun was analyzed based on the theory of the adiabatic compression and conservation of angular momentum. A series of initial parameters of 55 GHz double anode magnetron injection gun were obtained by Matlab programming. Independent research and development of three-dimensional particle simulation software CHIPIC was used to carry out numerical simulation. The obtained simulation data were analyzed and optimized. High-performance electron beam was obtained with a ratio of transverse velocity to axial velocity of 1.44 and a maximum velocity spread of 5.8%. The beam could meet the requirements of 55 GHz gyrotron oscillator tube.