The invention discloses a preparation method of Beta-type aluminum hydroxide; seed mother liquor serves as the raw material, carbon dioxide gas is fed in to neutralize the raw material, serum is filtered, precipitated, washed and dried to obtain the Beta-type aluminum hydroxide. The preparation method takes the seed mother liquor obtained from filtering seed aluminum hydroxide through a sinteringmethod, the produced Beta-type aluminum hydroxide has high purity and large specific surface area; and the mother liquor is returned to the preparation of the aluminum hydroxide through the sinteringmethod to participate in mixing, so that the circulation efficiency is improved and the main production cost is reduced.