Hydration lubrication plays an important role including the cartilage of an organism. Here, polystyrene nanospheres modified with a hydrophilic polymer through subsurface-initiated grafting as a biolubricating additive is proposed. The material provides good tribological performance when subjected to high load. Compared with surfaced-initiated grafting polymer brushes, subsurface initiation can form much thicker hydration layers to obtain a lower friction coefficient and better mechanical properties for withstanding prolonged shearing forces with less measurable damage. The polymer brushes penetrate through the covalent network of the polystyrene nanospheres providing a match in mechanical properties between them, so that the additives obtain more excellent lubricity in an aqueous environment under shear pressure, which is expected to become a promising artificial joint biolubricating additive.