Abstract: Determining boundaries of subcompartments is the foundation of forest resource inventory, which related to the accuracy of spatial location of forest distribution and precision of the number of area. The traditional way of the boundaries determination of subcompartments is based on the method of opposed sloping and drawing on the topographic map, this approach is subjective in some extent，and needs a lot of field surveying works. In a mountain area, boundaries of subcompartments, ridge and valley axes are coincident in generally, according to this characteristic of forest subcompartments，this study firstly extracted the valley and ridge axes based on the DEM data by applying hydrologic simulation methodology. Furthermore, with the integration of SPOT5 image, this study applied the image segmentation technique to determine the boundaries of subcompartments automatically, and assesses the accuracy of extractions, which could be up to 0.579.