Two imidazoline quaternary ammonium salts,OMAS and TMAS were prepared by diethylenetriamine reacting with oleic acid,twelve hydroxy stearic acid respectively,and their structure was characterized by Fourier transform infrared spectroscopy.Using simulated seawater instead of water as base fluid,the properties of two additives in the base fluid,including friction reducing,antiwear and carrying capacity,were evaluated by a four ball tribotester.The worn surface was characterized by scanning electron microscope(SEM),energy spectrum(EDS) and Xray photoelectron spectroscopy(XPS) test.The results show that the effect of friction reducing and antiwear of the base fluid is improved remarkably when the mass fraction of the additives is 10%.Compared with the base fluid,the bearing capacity of the base fluid containing OMAS is increased by more than 1 times,while the bearing capacity of the base fluid containing TMAS is increased by more than 9 times.The friction reducing and antiwear,and the bearing capacity of TMAS are better than that of OMAS,which is because that the imidazoline quaternary ammonium salt containing the hydroxyl side chain has stronger bonding or adsorption capacity than the imidazoline quaternary ammonium salt containing the unsaturated bond side chain,which is more easy to form the film on the metal surface.The results of XPS and EDS analysis show that a protective coating is formed on the metal surface by two kinds of additives through friction chemical reaction or adsorption,which improves the effect of friction reducing and antiwear of the base fluid.