The invention discloses a composite nano coating for oil casing threads. The composite nano coating comprises the following components: film-forming resin, an organic solvent, nano lubrication packing, a dispersing agent and a defoaming agent. A preparation method comprises the following steps: 1) uniformly mixing the nano lubrication packing and the dispersing agent; 2) grinding the mixture and the organic solvent, and uniformly mixing; 3) adding the film-forming resin, and uniformly mixing; 4) continuously adding the solvent till appropriate concentration, and uniformly mixing; and 5) sealing and storing the prepared coating. The use method of the coating comprises the following steps: 1) pretreating the oil casing threads, including decontamination, degreasing, washing with water, pickling and sand blasting or phosphorization; 2) coating or spraying the uniformly mixed coating on the surfaces of the threads; and 3) curing the coating at the room temperature. The composite nano coating disclosed by the invention is simple in preparation process, convenient to construct and low in cost, thread gluing is effectively avoided, and the threads are prevented from corrosion.