The invention relates to the technical field of inorganic matter preparation, and provides a method for preparing micro-nano aluminum oxide from an aluminum alloy hydrolysate, and the method comprisesthe following steps: (1) sequentially drying and ball-milling the aluminum alloy hydrolysate to obtain a ball-milled product; (2) carrying out solid-liquid separation on the ball-milled product, collecting a solid, and drying to obtain the micro-nano aluminum oxide, wherein the aluminum alloy hydrolysate in the step (1) comprises Al (OH) 3 and AlOOH. Compared with the disclosed aluminum oxide preparation method, the preparation method provided by the invention has the advantages of low raw material cost, simple preparation method process, easiness in operation and the like, and the method provided by the invention is beneficial to promoting the development of the field of aluminum alloy hydrolysis hydrogen production.