Through the hydraulic lubrication oil spectrometric analysis,we monitored the state of the power-shift steering transmission (PSST) equipped on the track armored vehicle for a long time.Combined with the friction material analysis inside the PSST,based on the concentration analysis of the wear and tear particle inside the oil,the authors estimated the wear and tear state of the PSST and judged if the PSST had the fault hidden trouble.So we can avoid the serious fault,provide the academic and actual basis for RCM and enhance the dependability for the track armored vehicle.The result of examples proves that the characteristic parameter of oil spectrometric analysis has very high stability and veracity.This method has proved effective in fault diagnosis based on oil spectrometric analysis on multifarious power-transmission systems in our army.This method is a breakthrough of the traditional maintainance model and has great useful military values.