Despite graphene's exceptional lubrication performance, its dispersibility issues limit practical application. Moreover, the synergistic lubrication mechanisms between nanomaterials and lubricants are unknown. Herein, we prepared a self-dispersible nanocomposite by mechanically mixing 3D porous graphene and TiO2 nanoparticles. The material demonstrated long-term stability in castor oil for over three months. A good synergistic effect of 3D porous graphene and TiO2 nanocomposites was found to significantly improve the extreme pressure (150%), friction reduction (25.13%) and anti-wear (30.63%) properties of castor oil. The friction and wear reduction are attributed to the interlayer sliding, ball-rolling effect of the G@TiO2 sheet-sphere-sheet structure and self-healing effect. Particularly, theoretical analysis revealed for the first time a novel mechanism: graphene's sliding on contact surfaces and within layers prevents excessive shearing of the oil film, enhancing its strength, thus improving load-bearing capacity and lubricity.