Abstract: The addition of various extreme pressure and antiwear additives in lubricating oil is an important and effective way to reduce friction and wear.Sulfurized olefin (SO) is used widely as an extreme pressure additive.The effectiveness of SO is attributed to the chemical reaction with iron to form an iron sulfide film.Brush plating is a special kind of electroplating.The Ni P and Ni Cu P brush plating layers show very good properties of anti scuffing,anti wear and reducing friction.But the lubricating behavior and mechanism of SO on Ni P and Ni Cu P plating layers are less studied so far.The tribological behavior of SO on Ni P and Ni Cu P brush plating layers was studied systematically on a ball on disc testing machine,and that of SO on 45 # steel was also studied for the sake of contrast.The composition of boundary lubrication films on disc worn surface was analysed using X ray photoelectron spectroscopy and Auger electron spectroscopy methods.Then the lubricating mechanism of SO on Ni P and Ni Cu P brush plating layers was discussed.It was found that the load carrying capacity of Ni P brush plating layer was increased obviously and the wear rates of Ni P and Ni Cu P brush plating layers were decreased very much with the addition of sulfurized olefin in lubricating oil.The chemical reaction film of NiS formed by the reaction of SO with the two brush plating layers on their wear surface possessed very good properties of anti scuffing and antiwear and a definite effect on reducing friction.