The invention discloses a modified nylon powder coating and a preparation method thereof. The preparation method comprises the following steps of: firstly preparing a polymerization product by performing polymerization reaction on the following main synthetic materials in parts by mass: 50 to 80 parts of caprolactam or nylon 6 resin, 20 to 50 parts of nylon 66 salt, nylon 66 resin or equal mole ratio of hexamethylene diamine and hexanedioic acid, and 0.02 to 1.7 parts of an auxiliary agent; and then preparing the modified nylon powder coating through the processes of extrusion modification, deep cooling crushing and treatment with a powder surface treatment agent. The auxiliary agent comprises an antioxidant, a nucleating agent and a molecular weight adjusting agent. The modified nylon powder coating prepared by the method is lower in melting point, simple in process control and stable in product quality, can partially substitute nylon 11 and nylon 12 powder products, can effectively reduce the using cost of nylon powder, is favorable for application popularization of the nylon powder, and has a great market potential.