Abstract:An aviation lubricating oil is mainly composed of polyαolefin (PAO) as base fluids and Nphenylαnaphthylamine (T531) as antioxidant. By stimulating temperatures of an aviation engineer in a high temperature and high pressure autoclave, the influence of antioxidant T531 under different temperatures on the physicchemical property of PAO was researched, the changes of compounds and structures were analyzed by joint technologies of GC/MS at molecular levels, and the thermal degradation mechanism of PAO and T531 was investigated. The results show that the molecular chain breakage and the oxidative reactions of PAO base fluids were prominent at high temperature, which caused reducing of lubricant viscosity and raising the acid value of PAO. T531 is helpful to T531 is quite helpful to slow down the molecular chain breakage of PAO in a certain temperature range. T531 is also degraded at high temperature for a long time, and a large number of chain ketones compounds are produced, which leads to the color deepening of lubricating oils.