Authors create a relief segmentation method on point cloud model, and solve such problems as how to store the point cloud data, how to obtain the final contour, how to define Snakes energy term and how to acquire region from its contour. Firstly, the point cloud data is resampled by applying Z-MAP grid data structure. Then initial contour is drawn by interaction, and the total energy of the contour is computed to optimize the contour to the energy-minimizing position by iterations. Finally, the contour is scattered as points, and the points are mapped to Z-MAP grids for projection points. According to these projection points, the region is obtained.