This article proposes modification of TiN nanoparticles via the sol-gel method and grafting reaction to prepare TiN@SiO2 nanocomposites (TiN@SiO2-RC), which was added into 85W90 gear oil as lubricant additive. The microstructure and oil dispersion stability of these nanocomposites were analyzed using transmission electron microscopy, potentiometer, infrared spectroscopy, and X-ray diffraction. Additionally, the tribological performance of these oils was evaluated using a four-ball friction and wear test machine. The 2D and 3D morphology, elemental composition, and chemical states of the worn surface on friction pair were comprehensively analyzed using scanning electron microscopy, 3D confocal microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Results show that the modified TiN nanoparticles exhibit considerably better dispersivity and stability than original TiN nanoparticles in 85W90 gear lubricating oil. At a mass concentration of 0.4 wt%, the 85W90 gear oil containing TiN@SiO2-RC achieved a substantial reduction of up to 14.6 % in the friction coefficient and a remarkable decrease of up to 23.2 % in the wear scar diameter. Notably, the nano-additives on the friction surface underwent chemical reactions to form reactive films, while the nonreactive nanoparticles mainly contributed to the formation of physical deposition films and acted as rolling bearing, improving the overall friction-reducing and antiwear properties.