Isoscallop height toolpath planning method is a high-efficient way to generate toolpaths. However, for some sculptured surfaces, the toolpaths generated via this method may be not smooth, e.g. the cutting direction may alter sharply which badly affecting the machining surface quality. If the curvature of toolpaths can be restricted, paths will be smooth and surface quality can be guaranteed. On the other hand, the machining efficiency may decrease comparing with toolpaths generated via Isoscallop height method. To balance efficiency and surface quality, a modified isoscallop height toolpath planning method based on curve fitting is proposed in this paper. Toolpaths generated via the new method can keep smooth and the efficiency is as high as possible under the restriction of the curvature set by users.