Abstract: The surface iso-segmentation method with conditions as input has applicability to different segmentation situations, however, does not thoroughly investigate its boundary point (BP) tracking procedure. Therefore, we present a BP tracking algorithm for surface iso-segmentation. Firstly, the BP tracking algorithm tracks BPs by repeatedly selecting the in-BP and out-BP of the current grid unit, constructing the subsequent grid unit and setting it as the current grid unit. Secondly, the key techniques of the algorithm including grid unit dynamic construction and the in-BP and out-BP selection of grid units by reasonably predicting the boundary curve (BC) growing trend are then systematically explored. Finally, attributes including coordinate, machinability, normal, Gaussian curvature and mean curvature are used to design 5 condition sets for the iso-segmentation of several CAD surfaces. When each grid unit has only 2 BPs, our method has the same segmentation accuracy with the existing method. When there exists a grid unit which has more than 2 BPs, the average BP deviation of our method is 91.78% lower than that of the existing method. Test results show that the proposed method suits for more complicated segmentation problems, and can achieve more precise segmentation and higher robustness.