Disclosed is nanocoupling of a polymer onto a surface of a metal substrate for improving coating adhesion of the polymer on the metal substrate, and in vivo stability and durability of the polymer. In accordance with the present invention, the polymers can be grafted via a chemical bonding on the surface of the metal substrate by the nanocoupling, by which adhesion, biocompatibility and durability of a polymer-coated layer which is to be formed later on the metal substrate were remarkably improved; therefore, the nanocoupling according to the present invention can be applied to surface modification of a metal implant, such as stents, mechanical valves, and an articular, a spinal, a dental and an orthopedic implants.