The invention discloses a film former for seed coating and the preparation method thereof. The preparation method comprises the steps as follows: subjecting diacetone acrylamide and unsaturated monomer to copolymerization reaction to obtain polymer, and reacting with dihydrazide compound to obtain film-forming material for seed-coating. The unsaturated monomer compound can be one or more selectedfrom methyl methacrylate, styrene, vinyl acetate, vinyl chloride, maleic anhydride, N-vinyl pyrrolidone, vinylidene chloride, acrylonitrile, methyl vinyl ketone, methacrylic acid, acrylamide, methyl acrylate, ethyl acrylate, butyl acrylate, dihydrazide, N-vinylcarbazole and butadiene. The film former prepared by the method has good film physical chemical properties such as forming property, waterresistance, air permeability, water permeability, etc., and drug slow release function to prolong drug effect and protect healthy growth of crops.