Aiming at the features of various failure types and complicated fault models in the vacuum system of space environment simulator, this paper studies fault diagnosis method for vacuum pump according to the feature of fault characteristic signal. Model-based parameter estimation method is used for the pressure signal in the container while adaptive threshold judgment method is utilized for time-domain signals, pump case temperature and the pump electricity, to make the fault diagnosis. The simulation results show such method can diagnose the four kinds failure modes, air leakage, low rotate speed in the vacuum pump, high temperature of the pump case and the abnormal incoming current into the pump. It is an effective method for making the fault diagnosis for the vacuum pump.