To realize high-quality functional structures in ceramic materials， a short-pulse ultraviolet nanosecond laser was used to study the application of laser micromilling technology in the fabrication of blind holes in Al₂O₃ substrates. The influence of the laser-pulse energy density， scanning speed of scanner， and total number of repeat scanning on the taper angle of the hole and bottom surface roughness was investigated using field lenses of different focal lengths in the milling experiment. The experimental results show that the focal length plays a significant role in the micromilling process， while the other parameters can be used for optimizing the processing quality. Therefore， appropriate selection of the optical focal length can effectively improve the processing quality of micromilling blind holes， in particular， their taper angle. A blind hole with minimum taper angle of 5.4°， a hole depth of 0.83 mm and a bottom surface roughness of 2.48 μm was achieved at a focal length of f =160 mm with a laser-pulse energy density of 25.80 J/cm²， a scanning speed of 1000 mm/s， and a total number of repeat scanning of 400.