The invention relates to a preparation method of a polymerizable quaternary ammonium cationic monomer, wherein the preparation method comprises the steps: mixing a solvent and acrylic acid, dropping aNaOH saturated solution, heating up and dropping a 3-chloro-2-hydroxypropyltrimethylammonium chloride solution, and carrying out a reaction for 4-6 h at the temperature of 55-75 DEG C; after the reaction is finished, cooling, and carrying out reduced pressure distillation to remove the solvent, to obtain a monomer crude product; and cooling, then adding a benign solvent for dissolving, carrying out suction filtration, collecting a filtrate, concentrating, cooling, then adding a poor solvent, separating out a precipitate, and drying to obtain a white solid product. The solvent is one of absolute ethyl alcohol, acetonitrile, acetone or isopropanol, the volume ratio of the solvent to water is 1 to 1, the molar ratio of water to acrylic acid is 16.6 to 1, the molar ratio of acrylic acid to sodium hydroxide is 1 to 1, and the molar ratio of CHPTAC to acrylic acid is (0.8-1.3) to 1; the reaction operation is simple, the yield is relatively high, and the synthesized polymerizable qauaternaryammonium cationic monomer has the advantages of richer adsorption groups, good water solubility, and high polymerization activity, and can further enrich the types of cationic monomers for polymerization.