The invention belongs to the technical field of new material preparation and lubricating oil additives, and discloses a nanometer copper / graphene composite material and a preparation method and application thereof. The preparation method comprises the following steps of: firstly dissolving a copper precursor compound, a surface active agent and a complexing agent into reducing alcohol, then adding graphene oxide, and carrying out ultrasonic dispersion to obtain a mixed solution; then adding a reducing agent to the mixed solution, transferring into a reaction kettle, introducing CO2 gas, and controlling gas pressure and temperature so that CO2 achieves a supercritical state; stirring the mixed solution inside the reaction kettle for reacting, cooling, decompressing, washing by centrifuging, and carrying out vacuum drying to obtain the nanometer copper / graphene composite material. The preparation method disclosed by the invention is simple, saved in time and fast. The prepared nanometer copper / graphene composite material has the characteristics of single phase, controllability in loading capacity, small nanometer copper particle size, uniformity in nanometer copper distribution on the surface of a graphene nanometer layer, and the like, has a synergetic lubricating effect, and can be used for outstandingly improving the antifriction and abrasion-resistant property of basic lubricating oil.