Abstract: The mechanical vibration state of hydropower unit is an important embodiment of its stability. It is of great significance to carry out mechanical vibration state evaluation of hydropower units based on the start-up dynamic process. Firstly,according to the characteristics of rapid dynamic change of speed during startup,an amplitude frequency feature extraction method of variable speed dynamic signal based on hardware order tracking and order analysis is proposed,and two mechanical vibration state samples of vibration peak and peak trend and characteristic frequency amplitude trend are constructed. Secondly,the distance measurement method in data mining is introduced to construct the key performance index of mechanical vibration state evaluation based on the change trend of the unit peak value and multivariate characteristic frequency energy ratio. The data of a hydropower station unit after overhaul are verified and analyzed. The results show that this method can effectively track,monitor and evaluate the change trend of mechanical vibration state of the unit,find the possible safety hazards in the early stage of startup,and serve as a guide to the safe and stable operation of the unit.