The invention relates to an aluminum nitride ceramic substrate line etching method. The aluminum nitride ceramic substrate is an active brazing ceramic substrate, the etching is carried out in two steps, the alloy brazing filler metal layer is etched in the first step, and the interface reaction layer of the brazing filler metal and the ceramic is etched in the second step. In the first step, theetching solution is composed of nitric acid and hydrogen peroxide, wherein the volume ratio of nitric acid to hydrogen peroxide is 0.3-2: 0.8-1.5, the mass concentration of the nitric acid is 65%-70%, and the mass concentration of the hydrogen peroxide is 20%-40%. In the second step, the etching solution is composed of sulfuric acid, hydrogen peroxide and water, wherein the volume ratio of sulfuric acid to hydrogen peroxide is 0.5-2: 0.3-1.5:0.1, the mass concentration of the sulfuric acid is 98%, and the mass concentration of the hydrogen peroxide is 20%-40%. According to the invention, a novel formula etching solution is adopted, the brazing layer and the interface reaction layer of the active brazing heat dissipation substrate can be selectively removed, the etching rate is high, and high-precision and efficient etching of the ceramic substrate is realized.