Abstract: Lithium grease with nano-tungsten disulfide as lubricating additive was prepared in this study. The optimal SRV- tribometer was employed to investigate the influence of nano-tungsten disulfide powder on the tribological properties of lithium grease. The micro-morphology, chemical composition and chemical state of worn surface were characterized by using scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. And the lubricating mechanism was analyzed. The results show that the tribological performances of lithium grease were greatly improved by adding nano-tungsten disulfide powder. In the friction process, adhesion and deposition of the nano-tungsten disulfide powder on the tribo-surface gave birth to the tribo-chemical film composed of Fe₂O₃, FeSO₄, WO₃ and Fe₃O₄ at high local temperature and heavy load. The good tribological performance was contributed by the tribo-chemical film.