The invention discloses a modified material used for water-proof paint and a preparation method thereof. The preparation method comprises the steps that 1, under the presence of a solvent, zinc chloride and alkali are mixed under a stirring condition to prepare mixed liquid M1; 2, sodium polyacrylate and a coupling agent are added into the mixed liquid M1 for mixing to prepare mixed liquid M2; 2,the prepared mixed liquid M2 is calcined after being dried, so that the modified material used for the water-proof paint is prepared. According to the modified material used for the water-proof paintand the preparation method thereof, the zinc chloride and the alkali are subjected to stirring and mixing reaction under the presence of the solvent, then the sodium polyacrylate and the coupling agent are added into the mixed liquid to conduct certain modification on particle surfaces, thus a layer of covering film is formed on each particle surface, furthermore, by adding the coupling agent, coupling agent chains can be formed on the particle surfaces, the particle surfaces can be modified better, and furthermore, the mixed liquid is calcined after being dried so that the prepared modified material can effectively improve the water-proof performance of the paint when used in the paint.