The invention belongs to the technical field of chemical preparations, and relates to an aluminum etching agent and a preparation method thereof. The formula of the aluminum etching agent comprises the following components in percentages by weight: 70-78% of phosphoric acid, 5-6% of nitric acid, 6-10% of acetic acid, 1-5% of sulfamic acid, and the balance of water. The aluminum etching liquid provided by the invention can convert a metal compound into soluble salts which are dissolved in water, speeds of etching to different metals are consistent basically, reaction is stable, the circumstance that etching efficiency and neatness of the surface of a substrate are affected by precipitate attachment is avoided, and surface dirt is removed conveniently.