Abstract: In order to explore the effect of diamond nanoparticles on the contact stiffness of tooth surfaces, based on the Hertz contact theory, a contact model of micro-convex body and a mixed lubrication model were established to solve the contact stiffness of tooth surfaces under different percentage content of nanoparticles and different rotating speed. The results show that the suitable percentage of nanoparticles is 10%~15%, and the relatively satisfactory contact stiffness of tooth surface can be obtained. The contact stiffness of nanoparticles and oil film stiffness decreased with the increment of rotating speed which led to the decrease of contact stiffness of tooth surfaces.