The invention discloses a preparation method of an efficient fire extinguishing superfine dry powder extinguishing agent. The preparation method comprises the following steps of uniformly mixing monoammonium phosphate, ammonium chloride, light calcium carbonate, dolomite powder, dicyandiamide, phenolic resin, magnesium chloride, borax, copper acetate and trimethyl ethyoxyl silane, carrying out warming, spraying methyl phenyl silicone oil in a stirring state, and uniformly stirring the mixture to obtain a mixed material; and crushing the mixed material, adjusting the temperature, and stirring and drying the mixed material to obtain the high-efficiency fire extinguishing superfine dry powder extinguishing agent. According to the preparation method of the efficient fire extinguishing superfine dry powder extinguishing agent, the water repellent property, fluidity, the jetting property and the anti-caking property of the obtained dry powder extinguishing agent are excellent, the price is low, furthermore, the specific surface area is large, fire extinguishing efficiency is high, the use amount is less during the extinguishing process of the fire disaster with the same level, and the fire extinguishing cost is low.