Electrochemical machining (ECM) is a method based on electrochemical process for removing metals in mass productions. In weapons industry, the project of ECM of chamber body cavity was put forward for its high precision and no cutting stress. According to research object—chamber body cavity, ECM device was designed, which were the inner cavity of ECM. Thereinto, with the use of the parallel gap method, the polishing cathode and the processing cathode of the complex inner cavity were designed; in consideration of the design of the two sets of fixture were done for the external shape of chamber body, and the base of the fixture should be equipped with a conductive seat; in addition, what needed to be considered were the relative problems of the electricity conduction, the feed liquid, the flow distribution and the insulation sealing between work pieces and fixtures. Among them, the method of the feed liquid lies in side streaming; the conductive method was to transmit the electric current to the workpiece through the galvanical fixture, and the conduction of cathode was through the draw bar which connected to the spindle. Under the fixture seat, an insulating board was added to bring about the insulation effect. The way to prevent the electrolyte from overflowing is to fill the gap between the draw bar and the end face of the fixture with a sealing gasket. Experimental results indicate that chamber body cavity can be produced at one time with good quality and high efficiency.