With the rapid development of 5G communication technology, terahertz wave has attracted extensive attention due to its large capacity, good directivity and strong anti-interference ability. However, in the terahertz communication system based on the subharmonic mixing method, in the process of generating the terahertz signal, due to the high frequency multiplication, the floor and phase noise of the original frequency source pass through the frequency doubling and amplification links, and the spectrum is realized. The shifting and amplification are degraded, while the circuitry of the link itself also produces an in-band noise superposition. In order to reduce noise, this paper studied on the basis of the principle of harmonic mixing terahertz communication system of the high harmonics and the vibration noise impact on the quality of communication, this paper proposes a method of harmonic interference suppression method this method by selecting the required harmonic band-pass filtering, set the appropriate frequency range can make other harmonic component to fall outside the frequency band, so as to achieve effect of reducing the noise of a terahertz communication system.