A new model referring to the relation of CSA and CSD was proposed,which was based on the physical mechanism for the origin of river heads.The feasibility of the model was verified by using two watersheds of Duilongqu basin of Lhasa River and Beishuiqu basin of Niyang River in Tibet to calculate the CSA and extract river networks.The comparison results of river networks derived from DEM with real ones indicated that the critical support discharge Q_c are (0.002 8 0.001) m~3/s in Duilongqu and (0.008 50.001) m~3/s in Beishuiqu,respectively.The CSD can vary with hydro-climate conditions. It was higher in humid region and lower in arid region.Using this method, the optimal critical support discharge Q_c of 0.008 5 m~3/s in Beishuiqu basin (humid region) was greater than 0.002 8 m~3/s for Duilongqu (semi-arid region).The suggested method provided a new application approach that could be used to determine CSD (Q_c) in complex geographical regions,and the effect of hydro-climate change could be reflected.