In order to investigate the effects of polyα-olefin (PAO) chain length and graphene additives on the tribological behaviors of synthetic base oil PAO,the tribological behaviors of PAO with different chain lengths were studied by molecular dynamics method.The effects of PAO molecular chain length and the mass fraction of graphene on the shear stress,van der Waals energy and oil film thickness between lubricating oil and rubbing pairs were studied.The results show that graphene can increase the van der Waals energy between the lubricating oil and the contact surface of the friction pair,so as to adsorb more lubricating oil molecules,increase the thickness of the oil film,reduce the shear stress and improve the anti-friction effect of the lubricating oil.The graphene also can make the change of van der Waals energy more stable and improve the adsorption stability of lubricating oil.The effects of graphene on PAO with different chain lengths are different.For the short chain PAO,a good anti-friction effect can be achieved only dding a small amount of graphene,the anti-friction effect is more obvious.However,for the long chain PAO,the anti-friction effect can be achieved only when the content of graphene is high.