A self-adjusting power device for high efficiency electrical discharge machining and method thereof is disclosed. A high-voltage arc unit and a low-voltage discharge unit provide a high voltage arc pulse and a low voltage discharge pulse to an electrode respectively. The electrode machines a workpiece and feeds back a gap voltage to a discharge pulse generation unit. The discharge pulse generation unit determines whether the gap voltage is lower than a predetermined voltage or not. If yes, a discharge channel between the electrode and the workpiece is conducted, and the discharge pulse generation unit shuts down the high-voltage arc unit and the low-voltage discharge unit is still operating at ON time and shuts down at OFF time. If no, looping the determination of the discharge pulse generation unit. Therefore, discharge machining energy is accurately controlled and high efficient power saving is achieved.