Abstract: The anti-wearing and friction reducing mechanism of lubricating oils with nano-particles was discussed by adopting scanning electron microscope,energy dispersion spectrum,X-ray photoelectron spectroscopy and atomic force microscope.The results show that nano-particles take the effect of the anti-wearing and friction reducing by the following five aspects such as “tiny polishing”;“tiny ball bearing”,which can support loads;filling in and repairing worn surfaces;synergistic effect of big and small nano-particles and the new metal element and oxide film produced on the friction surface,which can protect the friction surface.