The work aims to provide reference for controlling burrs on aluminum alloy 6061, improving surface quality and optimizing cutting process by revealing law of influences of milling process parameters (cutting depth ap, feed per tooth fz and cutting speed v), down and up milling methods as well as tool wear on burr size and shape during micro milling of aluminum alloy 6061. Based on single-factor test method, milling processing test was performed to aluminum alloy 6061 with micro-diameter cutter for coated carbide, so as to collect and analyze such information as top burr size data, tool wear and burr shape for the single-factor test. A diagram indicating law of influences of ap, v and fz on the top burr size ob both sides of up/down milling was visually plotted. In the single-factor cutting speed test, the maximum burr size was 323 μm on down milling side and 268 μm on up milling side; in the single-factor feed per tooth test, the maximum burr size was 332 μm on down milling side and 331 μm on up milling side; in the single-factor cutting depth test, the maximum burr size was 314 μm on down milling side and 264 μm on up milling side. Top burr size on up milling side is smaller than that on down milling side. With the increase of cutting depth, burrs appear to be long fibrous, tearing and wavy serrated shape successively. Tool wear is an important factor leading to unstable cutting process. It can also cause unstable burr shape and size. Adopting sharp tools and up milling, controlling cutting depth and selecting proper cutting speed and feed rate contribute to minimization of burrs.