The embodiment of the invention relates to an electric spark machining device and further provides a method for machining a workpiece through an electrode assembly. The electric spark machining device comprises the electrode assembly. The electrode assembly comprises a pedestal provided with a plurality of electrode supports. A plurality of electrodes can be detachably contained by the multiple electrode supports correspondingly, and the multiple electrodes comprise the multiple first electrodes and the multiple second electrodes. The multiple first electrodes are used for conducting rough machining on the workpiece in an electric spark machining mode or in a wire-electrode cutting electro-discharge machining mode so as to remove materials from the workpiece. The multiple second electrodes are used for conducting finish machining on the roughly-machined workpiece in an electric spark machining mode to remove materials from the roughly-machined workpiece.