The invention relates to a method for preparing an aluminum nitride ceramic substrate and belongs to the technical field of electronic ceramic preparation. The method comprises the steps of 1, preparing tape casting slurry; 2, tape casting, wherein the tape casting slurry prepared in step 1 is subjected to vacuum defoaming and then enters a tape casting machine so that a tape casting blank can be obtained through tape casting; 3, stamping, wherein the tape casting blank is stamped into uniwafer blanks; 4, solvent coating, wherein the front side and back side of each uniwafer blank are coated with an organic solvent; 5, laminating, wherein the uniwafer blanks coated with the organic solvent obtained in step 4 are stacked and then subjected to vacuum packaging; 6, isostatic pressing; 7, tape ranking; 8, sintering, wherein the aluminum nitride ceramic substrate is obtained through sintering. By coating the contact surfaces of the laminated blanks with the solvent, the prepared blanks are uniform, and the sintered product has high compactness (determined by the tape casting technology), uniform appearance and uniform performance.