Abstract: The dual-frequency operation coaxial gyrotron with two electron beams is investigated in this paper. The results of the numerical calculation and particle in cell (PIC) simulation show that the coaxial gyrotron with two electron beams (CGTB) can operate at two different frequencies simultaneously. In addition, the power of the high harmonic can be enhanced due to the nonlinear coupling between two electron beams. The prototype of CGTB was fabricated and the verification experiment was conducted. The operation frequencies are at 0.11 THz and 0.22 THz, and the output power is about 20 kW. A method to separate the radiations from a dual-frequency operation gyrotron is also proposed.