WS2 film with excellent lubricating property was combined with lubricating oils (PAO, PFPE and MACs) with different molecule structures to construct WS2/oil composite lubricating systems, respectively. The influences of the molecule structures and properties of oils on tribological properties of the systems were investigated systematically in vacuum. The result indicated that the WS2/PAO and WS2/MACs systems exhibited the obvious synergistic lubricating effect under relatively harsh testing condition, markedly prolonging the lubricating life and decreasing the wear rate. There is a new discovery that numerous ultrasmall WS2 nanosheets were generated and uniformly adhered to friction contact area, further in-situ forming the tribolayer that significantly enhanced the lubricating life. The lubricating mechanism of the long lifetime for WS2/oil systems is finally revealed.