The invention relates to a preparation method of aluminum hydroxide, particularly a preparation method of high-dispersity superfine aluminum hydroxide. The method is characterized by comprising the following steps: carrying out two-stage seed decomposition by using nano active aluminum hydroxide prepared by the reaction between a sodium aluminate solution and an aluminum sulfate solution as a seed, carrying out solid-liquid separation and washing on the obtained decomposition pulp, and carrying out mechanical stirring and grinding to prepare the superfine aluminum hydroxide. The superfine aluminum hydroxide prepared by the method has complete crystal form, effectively solves the problem of aggregation of the superfine aluminum hydroxide, and solves the problem of secondary granularity caused by aggregation; and the method enhances the dispersity of the superfine aluminum hydroxide, and lowers the oil absorption number of the superfine aluminum hydroxide to 28-32ml/100g.