The invention discloses an electrode machining device of an electric spark forming machining tool and a use method of the device. The device comprises a body, a wire winding wheel, a wire unwinding wheel, a guide rail, guide rollers, a guiding wheel, a driving wheel, a resistance wheel, sliding guide rails and sliders. The body is fixed to a magnetic suction cup. The wire winding wheel, the wire unwinding wheel, the sliding guide rail, the driving wheel, the resistance wheel and the guiding wheel are fixed to the body. The functions of wire winding, wire unwinding, driving and constant tension force are achieved by means of the wire winding wheel, the wire unwinding wheel, the driving wheel and the resistance wheel respectively, it is guaranteed that electrode wire moving speed and tension force are constant and can be adjusted continuously, the structure is compact, and stability is good. By the adoption of design of a five-slider three-sliding-guide-rail combined module, different sliders are selected to participate in electrode wire moving to achieve single-wire and double-wire machining modes, and electrodes in different sizes can be machined by adjusting the positions of the sliders to adjust the interval of the guide rollers and the distance of electrode wires.