Above, we partially introduce the background of gear broken fault analysis method and the research status at home and abroad, and then look for effective statistical indicators to evaluate and estimate the trend of gear broken. Through the statistical analysis of vibration signal to analyze which index is better. According to the time-domain waveform, the statistical value obtained from the statistics of vibration signal data has been widely used in the fault diagnosis of mechanical equipment, showing the trend that the effective value changes with the crack size. RMS is the average value of the signal, which is used for the level test of the vibration signal. The formula is as follows: