Abstract: A magnetic field was assembled around the friction region in a four-ball tester. The tribological properties of 150SN base oil and lubricating oils containing tricresyl phosphate (TCP) under magnetic field were evaluated by the modified tribo-tester. The morphology and the chemical species of typical elements on the worn surfaces lubricated with the tested oil were examined by scanning electron microscope and X-ray photoelectron spectroscopy (XPS) to reveal the tribological mechanisms. The tribological test results indicate that the wear scar diameters of the worn surfaces lubricated by base oil and the TCP-doped oils under magnetic field were smaller than that under non-magnetic field while the friction coefficients of the tested oils under magnetic field were higher than that under non-magnetic field. The XPS results illustrate that the tribological performance of lubricating oils were related to the properties of boundary lubrication film. The improved anti-wear property of the lubricating oils containing TCP under magnetic field was attributed to the enhanced interaction between elements phosphorus and oxygen in TCP and metal surface, which gave birth to the tribo-chemical films.