Abstract: The authors provide a method to fit complex surfaces using Bezier surface theory. With this method, we can solve a kind of problem of getting complex surfaces by fitting the given scattered data poiats. In calculating the points of intersection of surfaces, a great deal of time has beensaved, due to widely using the segmentation theorem and its degenerative form. With these methods, the authors have made a surface CAD/CAM program system and successfully manufactured a mould of helical intake port of diesel engine on NC machines.