The invention relates to an electron gun matched with a cyclotron amplifier in the technical field of microwaves, which comprises an electron gun body used as an anode, an anode head, a mode conversion mechanism, a transition section, a cathode and a ceramic ring, wherein the anode head, the mode conversion mechanism and the transition section are arranged in the electron gun body; the cathode is arranged at the rear end of the gun body and shares the same axle line with the gun body; the ceramic ring is used for connecting the cathode and the gun body into a whole; and the cathode is also provided with a central hole and a waveguide tube which is connected with the central hole and used for signal input. The electron gun can generate an electron bunch with good performances of large working speed ratio and small electron bunch fluctuation and speed scatter and can also carry out dual functions of microwave input mode conversion and improve the conversion efficiency of the mode. Moreover, when the electron gun is matched with a resonant cavity, the electron gun can greatly improve the structure of the cyclotron amplifier so as to ensure that the cyclotron amplifier has the characteristics of simple signal input mode and structure, small volume, high conversion efficiency, lower requirement on the intensity of a working magnetic field, realization of the miniaturization of the cyclotron amplifier, effective reduction of the design difficult of a high-performance cyclotron maser device, and the like.