[Objective] Method of determining appropriate drain area threshold was demonstrated to reflect the actual river drainage network.[Methods] Based on the DEM data of Longchuan River basin, the automatic extraction module of watershed drainage network in ArcGIS software was used to extract relevant drainage information. After that, a function between river network density and catchment threshold was fitted, which was used to determine the appropriate drainage threshold by finding the turning point of its first derivative function and/or the inflection point of the second order derivative. This was simultaneously exemplified by the Longchuan River basin. In this case, the threshold was determined by finding where the ratio change of river network density equal to the change rate of the water drainage threshold.[Results] The river networks under different catchment drainage threshold were compared and found that no obvious differences existed with regard to the catchment threshold length of the main channel and the geographic location, but other features of river network were apparently different. In the case of the Longchuan River basin, its appropriate threshold was thought to be 0.12 km².[Conclusion] The river network extraction precision varied with the drain area threshold. The proposed method in the determination of the catchment threshold is less subjective, and is more objective, which can be used to provide some bases for the monitoring of regional soil erosion.