Aiming at the geometric contour machining of the noncircular curve, an optimal approximation point search algorithm based on error control was proposed, by which whole information of noncircular curve could be contained. An automatic NC programming system was developed, which integrated the noncircular curve approximation machining strategy, could automatically identify the noncircular curve,arc and line.The NC code can be used in multi system CNC machine tools, and can improve the efficiency and accuracy of complex products processing.