Abstract: Gear fault is the main form of gear box fault. Therefore, the judgment and analysis of gear running state is of great significance to reduce the gear box failure rate and prevent sudden accidents. This paper mainly introduces the application of spectral analysis method in fault diagnosis of gearbox gears. It summarizes the spectrum characteristics of common gear faults. Combining with the application examples, the paper analyses and diagnoses the gearbox breakage faults. The results show that spectral analysis can accurately judge the gear fault location and the severity of the faults. It can help the maintenance personnel to adopt the best maintenance strategy in combination with the actual running state, and provide an effective way for gear fault diagnosis.