Abstract: It is well known that tribology is an interdisciplinary subject.But most tribologyproblems were investigated usually from the aspect of a single discipline so far,due to theircomplexity,considering the conditions of other aspects to be constant and negligible. Such asituation is an obvious obstacle for solving more deeply the tribological problems. Therefore,theinterdisciplinery researches of tri bology are becoming more and more attractive to all tribologists.The addition of various extreme pressure(EP) and anti-wear(AW)additives in lubricating oilis an important and effective way to reduce friction and wear.The application of chemical heattreatments, such as sulfuration or nitriding on surface of materials is another effective way forimproving the tribological behavior of rubbing pairs. However,the combination of both way is stillless reported.In this paper,the synergistic effect of two additives sulfurized olefin(SO)and tricresylphosphate(TCP) in paraffin oil and ion nitriding treatment of 45# steel on the tribological behaviorwas studied systematically on a ball-on-disc testing machine. Excellent results were obtained for ionnitriding steel matched with EP and AW additives in increasing load bearing capacity and reducingfriction and wear.The mechan ism of this synergistic effect was discussed based on the micro-analysis of surface film by AES and XPS.