The working tooth of traditional cathode can’t change angle with the helix angle changing while processing mixed rifle, so the rifle would be widen and sunken. An assembled cathode comprising a cathode body and ten turntables with teeth was designed, which can do relative motion to body. The step between adjacent turntable teeth being a cause to induce cave and eddy, three schemes were adopted to optimize teeth shape and the gap flow field was simulated by COMSOL. The results show that the gap flow velocity bear on the shape of tooth, while the left side of which was chamfered (R0.24mm) and the right side screw out 0.15mm, the shape of tooth is considered appropriate. The simulation results are consistent with to the experiments.