The tribological properties of molybdenum dialkyl dithiocarbamate (MoDTC) combining with calcium and magnesium type detergents were investigated by fourball friction and wear tester.The worn surface of steel ball was analyzed by white light interferometer,scanning electron microscopy (SEM),energy dispersive spectrometer(EDS) and Xray photoelectron spectroscopy(XPS),and the tribological mechanism of the compound system was discussed.The results show that there is a synergism to some extent when MoDTC combining with calcium and magnesium type detergents,and the compound system composed of 0.3%~0.5% MoDTC and 03% ~05% detergents has more obvious friction reducing and antiwear performances.The reason is mainly due to the combined effect of the MoS2 chemical reaction film and the corresponding deposited film formed during the friction process.