The invention relates to a waterproof locking agent and a preparation method thereof and belongs to the technical field of a drilling fluid additive. The method comprises the following steps: putting acrylamide, distilled water, glycerin monostearate and cetyl triethyl ammonium bromide into a stirrer for stirring, collecting and mixing a mixture, thereby acquiring an emulsion; putting the emulsion, cyclohexane, liquid polybutadiene, ammonium metavanadate and neodymium oxide into a reactor, using nitrogen for protecting, preheating, adding ammonium persulfate and stirring; after ending stirring, raising temperature, stirring and reacting, cooling and then adding gamma-aminopropyl triethoxy silane, uniformly stirring, standing, cooling to room temperature and collecting a reaction mixture; performing reduced pressure distillation on the reaction mixture, removing distilled water and cyclohexane, collecting distilled residue, filtering, collecting filtrate, and uniformly stirring the filtrate and beta-sitosterol, thereby acquiring the waterproof locking agent. The waterproof locking agent prepared according to the invention can effectively reduce the tension on the filtrate surface and the tension on the oil-water interface and can increase the permeability of oil and gas phases.