Aluminum nitride (AlN) ceramic has excellent electrical insulation and dielectric properties. The ultra-precision lapping and polishing techniques for the AlN substrate are studied in this paper, and the influence of the lapping parameters such as load and slurry on the surface roughness, material removal rate of AlN is discussed. The surface of workpiece after processing is observed with microscope to analyze the material removal mechanism. An extremely smooth surface with roughness 6nm Ra is obtained after the finishing process. It is also found that the gap between grains will decrease the precision and quality of AlN substrate.