A micro drilling process using a turbine driven air spindle was developed to improve drilling quality.Some drilling experiments for drilling 0.5 mm holes magnesium alloy AZ31B sheet were carried out.The influences of rotational speed and feed rate on burr height at the exit of the micro hole,saperture error and roundness error at the entrance were investigated.The aperture error and the roundness error were obtained by the image processing and the least square method.Drilling parameters were optimized synthetically.The results show that performance of the spindle is in a good condition.When the rotational speed is 20 000 r/min and the feed rate is 0.4 mm/s,the comprehensive quality of micro drilling reached the best.