Abstract: Extraction of geomorphic parameters is the foundation of constructing hydrological model,so the precision of extraction of geomorphic parameters affects the accuracy of hydrological model.This paper studied on the method of geomorphic parameters for Geomorpho-Climatic Instantaneous Unit Hydrograph(R-V GIUH) by DEM: dealing with the sink-filling problem of DEM;extracting channel network of different critical support area;analysing on the effects of the critical support area on both the total length and the average slope of the extracted channel network;determining the critical support area for channel development;calculating the geomorphic parameters of watershed for the convergence model of R-V GIUH. The method is applied in Fengjiageduo small watershed(17.98 km²).The results showed that the extracted drainage networks are reasonably close to the reality,and Horton's bifurcation ratio(4.608 3),area ratio(2.592 8),length ratio calculated(3.399 9) are in the proper range which is determined by analysing lots of data of nature water systems.The proposed approach removes the subjective decision on the choice of drainage area threshold,and improves exactness of extracting geomorphic parameters.