Abstract: In numerical control machining, arc fitting and spline fitting have curvature mutation, high computational complexity and machining speed fault. A fitting method using sine curve instead of arc curve was proposed to solve the problem. The three-dimensional four-leaf clover shape path set by ourselves was taken as the object for simulation analysis. The results show that both sinusoidal arc interpolation and arc interpolation have the advantages of high computational accuracy; the full length of sinusoidal arc interpolation's transition edge length is increased to 147.5%~218% of arc interpolation while the curvature is kept continuous. When limited by the same transition length, the Angle range of sinusoidal arc interpolation is increased by about 29%~46%. In the follow-up velocity planning, the backtracking method in velocity foresight is added, and the velocity fault and acceleration and acceleration overrun problems are solved.