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As an important and unique ditch control project in the severe soil erosion area of Loess Plateau, check dams have the functions of flood detention, silt retention, and water storage. However, when using digital elevation model (DEM) for watershed water system analysis in this area, the extracted channel network will be disturbed by the check dam to have offset and dislocation problems. An automatic method for detecting the check dam and correcting the DEM was proposed to realize the effective extraction of the channel network. In this method, using the region growing and morphological algorithms to extract the center line of the channel to narrow the detection area of the check dam. Based on the improved line segment detector (LSD) algorithm and angle filtering, the candidate outline line of the check dam was determined, and then a cross model was constructed to locate the check dam. Finally, the grid elevation where the check dam was located was corrected to obtain a complete channel network. The F1 values of check dams detected by this method in two typical sample areas of the Loess Plateau were 86.67% and 86.95%, respectively. Compared with the two channel network extraction methods of filling and breaching, the method can effectively solve the problem of channel deviation. The experimental results showed that the results of the channel network extracted were more consistent with the real topography, which can provide useful supplements and support for the digital terrain analysis technology of the Loess Plateau check dam area.