In this paper, not only a new system info for NC machining of contour curve based on vector synthesis interpolation of conic curves is proposed, but also the key technologies are researched. These key techniques mainly include the developing of NC system for vector synthesis interpolation of conic curves, designing of algorithm for conic curve approximating plane parametric curve and software for NC machining of parametric curve. At last, an example for NC machining of contour curve are showed to prove the accuracy of proposed method.