In response to the difficulties in machining cemented carbide, this paper proposes a new approach to electrochemical milling of cemented carbide. A composite rotating tool cathode for electrochemical milling is designed, and the electric field simulation calculation is conducted for the electrochemical milling process. The electric field results show that as the tool cathode continues to penetrate, the machining area of electrochemical milling continues to increase, and the current density in the machining gap increases. After the tool cathode enters the semicircle, if the processing area of electrochemical milling remains unchanged, the amount of material removed per unit time remains unchanged, and the current density also remains stable. At the same time, orthogonal experiments and process parameter optimization were conducted on the electrochemical milling of cemented carbide side edges. The results showed that the maximum material removal was achieved under the process parameters of processing voltage 14 V, feed speed 10 mm/min, spindle speed 3000 r/min, and duty cycle of 70%. Based on the optimized process parameters of side-edge electrochemical milling, full edge electrochemical milling of experiment was carried out. When the feed rate is 0.3 mm/min, the surface of cemented carbide electrochemical milling is relatively flat and has a roughness of 0.389 μm.