Abstract: Aiming at improving the interpolation efficiency without lowering the path accuracy, the velocity look-ahead control in CNC(computerized numerical control) was introduced. Firstly, the interpolation geometry elements linking vector angle model, which was separated into line-connect condition and circle-connect condition, was proposed. The CNC velocity look-ahead control algorithm was presented. This novel algorithm can find the approximate optimal velocity adaptatively based on the maximum number of look-ahead segments and the geometric properties of the interpolation path, then the high connected velocities between segments can be achieved. Because introducing the acceleration attenuation in acceleration zone and deceleration zone, the S-shape acc/dec(acceleration/deceleration) can improve the flexibility of interpolation. By combining the advantages of the look-ahead control algorithm and the S-shape acc/dec in high velocity condition, a novel S-shape acc/dec CNC look-ahead interpolation algorithm was introduced and realized. This algorithm feasibility has already been proved in real CNC system.