Abstract: The watershed topography is a key factor in the formation of the channel network and thus becomes a very important topic in the study of the digital basin and the distributed rainfall-runoff models. The widely used method for extracting the watershed channel network from digital elevation mo del (DEM), i.e. the water catchment area method, is presented. This method includes two steps: calculation of the water catchment area for each pixel of DEM, and determination of the critical support area (CSA) for channel development by analysis of the effects of the critical support area on both the total length a nd the average slope of the extracted channel network. The water catchment area method is employed to extract the channel network of a medium-size watershed wi th an area of 265 km2, and the extracted results are reasonably close to the reality. Because this method is automatically executed, it can be very useful in the analysis of the characteristics of the river networks of watersheds, especially for those uncharted regions.