Abstract: Turbine blades, working in high pressure and temperature environment, need repair regularly. To improve the efficiency of blade repair, an automatic method for broken boundary extraction is proposed in the paper. The extraction procedure consists of two steps: segmentation and boundary reconstruction. The segmentation extracts the damaged region from point cloud with the processes of curvature estimation, seed grid selection and region growing. This step can be completed in a short time through a 4D Shepard surface based curvature estimation method. In the second step, boundary reconstruction is approached by polygon subdivision and discrete fairing. A new global fairing indicator and a special given tolerance guarantee that boundary can be smoothed while preserving the required accuracy. The proposed method can perform without any user interaction, and it can also be used in other applications, such as the repair of molds and dies. Several examples are given to show its efficacy.