The invention discloses a method for making high-purity aluminum oxide by utilizing crystalline aluminum chloride. The crystalline aluminum chloride is the crystalline aluminum chloride in the production process of the aluminum oxide by a fly ash acid method. The method comprises the following steps: utilizing part of the crystalline aluminum chloride to prepare an HCl solution of saturated AlCl3, performing purification on part of the crystalline aluminum chloride to obtain primary purification aluminum chloride crystals, then utilizing concentrated hydrochloric acid to perform secondary purification on the primary purification aluminum chloride crystals, and then calcining and crushing the obtained aluminum chloride to obtain the aluminum oxide. According to the method disclosed by the invention, a small part of the aluminum chloride to be purified is consumed and a large part of the aluminum chloride is purified, so that the cost is saved; furthermore, the solution after purification can be recycled; and in addition, impurity removal is performed on the crystals in the two purification processes, the purity of the aluminum chloride crystals is improved, the crystals are of large particles, the sand-like aluminum oxide is obtained after calcination, and the product purity is more than 99.9%.