Experiments of micro-EDM in gas (dry MEDM) were conducted on the conditions of an external supplying gas mode based on a RC pulse generator. The objective of the work is to optimize machining parameters of the dry MEDM and investigate the machining performance of the ultrasonic induced workpiece vibration. Micro solid copper electrodes were fabricated on line by the block grinding method. Range analysis results of the Taguchi approach indicate that capacitance, servo feed speed have great effect on the material remove rate (MRR); and capacitance and open voltage are main influencing factors on the tool relative wear ratio (TWR). An optimal parameters combination was obtained under the experimental conditions. The experimental results of the ultrasonic induced workpiece vibration demonstrate that high frequency workpiece vibration with a suitable input current could improve MRR and TWR of the dry MEDM.