The invention relates to a preparation method of alumina powder. The preparation method of the alumina powder comprises the following steps: metal aluminum and a quaternary ammonium base aqueous solution react in a hot bath to prepare an aluminum hydroxide precipitate, the aluminum hydroxide precipitate is filtered, washed, dried, calcined at high temperature and crushed to prepare alpha-phase alumina powder and gamma-phase alumina powder, and the quaternary ammonium base aqueous solution is still used as filtrate capable of being repeatedly used. A quaternary ammonium base is an organic base with a structural formula of R1R2R3R4NOH, wherein R1, R2, R3 and R4 can be same (or different) alkyl groups (or aromatic groups). The invention has the advantages of low technological condition requirements, environmental protection, low cost and good product repetitiveness, is particularly suitable for mass production and can prepare high-pure ultra-fine alumina powder if high-pure aluminum sheets are adopted as an aluminum source, thereby being applied to the fields, such as high-voltage sodium lighting tubes, long-afterglow luminescent materials, tricolor fluorescent powder, advanced grinding materials, artificial lenses, and the like.