Abstract: A single-anode magnetron injection electron gun is designed and simulated according to the requirements of a 94 GHz gyrotron oscillator. On the basis of detailed theoretical analysis about the operating principle of the gun by programming, the designing of its initial parameters is performed, and its calculation module is developed based on the particle simulation software CHIPIC. The simulation results show that, the ratio of transverse velocity to axial velocity is 1.42 and the velocity spread is about 4.6%. The designed electron gun has achieved excellent beam parameters, which can meet the requirements for the electron beam in the gyrotron oscillator.