Abstract: The chemical reactivity, extreme pressure (EP) and antiwear (AW) properties of binary additive systems were investigated using hot-wire method and four-ball test machine. Auger electron spectroscopy was applied to analyze the element constitution of wire surface and the wear trace surface of steel ball after test for understanding the interactions between EP and AW additive and other type of additive on the iron surface. The results indicated that the antiwear properties of three EP and AW additives are apparently influenced by petroleum calcium sulphonate and benzotriazole hexade-camine, but the antiwelding property is not. During the reaction of EP and AW additives on iron surface the antiwear properties of three EP and AW additives reduce in the presence of petroleum calcium sulphonate owing to its intervention. Benzotriazole hexadecamine can improve the antiwear properties of three EP and AW additives because it enhances the chemical reactivity of additive to adequate level.