Abstract: The synergistic effects between three kinds of chemical heat treatment surfaces of 1045 steel,including oxy-nitrided, nitrided and sulfurized surfaces,and two kinds of extreme pressure (EP)-antiwear(AW) additives, sulfurized olefin and tricresyl phosphate, were studied systematically on a ball-on-disc testing machine. The composition of lubricating films on disc wear surfaces was analysed using X-ray photoelectron spectroscopy and Auger electron spectroscopy methods.The mechanism of the synegistic effects was discussed. It was found that exeellent synergistic effects on increasing load carrying capacity and reducing friction and wear could be obtained.