In this paper, to solve the problem that di-n-hexadecyldithiophosphate (DDP)-modified Cu nanoparticles initially used as oil-based lubricant additive cannot be directly used in water-based lubricants, we adopt a water-in-oil reverse micro-emulsion method to incorporate hydrophobic Cu nanoparticles into silica spheres for obtaining water-dispersible Cu@SiO2 nanoparticles. The effects of reaction conditions on the morphology and microstructure of Cu@SiO2 nanoparticles were investigated. Furthermore, the tribological properties of the as-prepared Cu@SiO2 nanoparticles as a lubricant additive in distilled water were investigated with a UMT-2MT tribometer. Results indicate that the as-prepared Cu@SiO2 nanoparticles exhibit good dispersion stability and antioxidant ability in distilled water. Besides, Cu@SiO2 nanoparticles can significantly improve the tribological properties of distilled water, which is attributed to the formation of a protective and lubricious film consisting of Cu, FeS and SiO2 on the rubbed steel surface.