Abstract: Although spectrometric oil analysis(SOA) is a widely applied technique for wear condition monitoring of lubricating system,this single monitoring technique is difficult to accurately predict some damages or failures in oil wetted system including bearing fatigues of aero-engine.In this paper,two techniques including SOA and auto debris classifier were applied to synthetically monitor a certain aero-engine,the Dempster-Shafer(D-S) evidence theory was used to implement fusion diagnosis,and an engine oil monitoring expert system was developed to carry out fusion diagnosis.Finally,some examples were analyzed;the results indicate that synthesized monitoring and fusion diagnosis is an important approach to increase the reliability for forecasting failures of aero-engine.