Two ionic liquids,matrine-6 and l-carnitine-citric acid,were synthesized,and their structure and thermal stability were analyzed.The lubrication properties of ionic liquid as lubricant were studied when Si3N4 ball was rubbing with metal substrates of 316 stainless steel,Al,Cu and Ti,and were compared with that of the Mobil No.1 oil.The results show that different ionic liquids have different lubrication effects on different substrates,and l-carnitine-citric acid has high bearing capacity,lower friction coefficient and high thermal stability,under its lubrication,the abrasion marks are more uniform and the wear volume is small.The lubrication effect of l-carnitine-citric acid is better than that of Mobil No.1 oil,because it forms effective physical absorption protective film and friction chemical reaction film in the process of friction,and forms more complex lubricating coating of iron-containing compounds,and the combination of the two improves the lubrication effect.