With the support of GIS technology，the SCS (soil conservation service)model was selected to model runoff of the upper watershed of the Luohe River(a tributary of the Yellow River) using a 1:250 000 DEM and a 1，1 000 000 DEM.By comparison of the simulated annual average runoff yield from through to 2000，it was found that a higher runoff volume was obtained using the 1:250 000 DEM.There are marginal differences in area，elevation，slope，channel length，and drainage network between the DEMs of different resolution，but there is a greater difference in slope change.Through analysis of the sensitive parameter CN of the SCS model，the sensitivity of runoff modeling to DEM resolution is described from the perspective of slope change.