Abstract: The extracting process can be divided into two stages：rough segmenting and refining.At the former stage,an optimal method based on curvature string-matching technique is put forward to find contour segments similar to the seed contour from another layer.At the later stage,based on turning angle mapping and B-spline fitting of planar curve,an approach to adjust the ends of the contour segment achieved at the former stage is put forward.As demonstrated in the presented examples,this paper solves the problem of exact contour segmenting of freeform surfaces,which paves a way for 3-D feature parameter identification and reconstruction of CAD models.