oxidative reaction of antioxidant Nphenylαnaphthylamine（NPAN）in polyαolefins（PAO）was studied by simulating test.The composition and structure of oil samples after oxidation at 200 ℃were analyzed by FTIR.The remaining content of antioxidant NPAN in PAO was measured by GC/MS.The results show that during thermaloxidative degradation of PAO,the changes of the kinematic viscosity of PAO and NPAN remaining contents have good correlation.With the large consumption of antioxidants,PAO begins to oxidize quickly and phenomenon of oxidation failure occurs.The thermaloxidative reaction of NPAN in this research is a pseudofirst order reaction.The kinetics of thermal oxidative degradation of NPAN can reveal the degrading of PAO,which provides basis for the quality monitoring of lubricating oils and the determination of reasonable drain intervals.