Abstract To solve the problem that positive string will fall down when cannon tube rifle becomes wider between the beginning segment and the changing tangle segment by using fixed cathode of ECM to machine big caliber and deep string groove cannon tube, the method by separating work teeth as discrete component and regarding it as a structure that connects but exists relative movement with cathode was adopted. Solid geometric model of cathode was established and work teeth, flow-guiding system and driving system were designed. When cathode was hauled by pull rod to axial feeding and radial direction, micro-motor embedded in cathode will drive independent work teeth according to program simultaneously. According to the change in trajectory equation, the work teeth keep consistent with the tangle. This method can realize highaccurately machining of cathode teeth．
