By using hightemperature oxidation accelerated simulation device,the variation of polyαolefin lubricating base oil under hightemperature oxidation was researched.By using FTIR and GC/MS detective methods,the composition and structure of hightemperature products and polyαolefin base oil was analyzed in order to discuss the influence of structural changes on lubricant performance and to speculate the hightemperature oxidation process and reaction type of lubricating base oil.Results show that serious thermal oxidation and thermal dissociation reaction are occurred under hightemperature,which causes the base oil color deepening,viscosity thinning and acid value increasing.Because of the unique structure of polyαolefin containing more tertiary carbon molecules,it is easily fractured under hightemperature to generate active free radicals.These free radicals are oxidized by oxygen to generate small molecules of aldehyde,ketone,acid and ester,which causes the acid value increase of lubricants.Meanwhile,the thermal dissociation is occurred at the same time and small molecular alkanes and alkenes are generated,which causes the viscosity decay of polyαolefin lubricating base oil.