The use of digital elevation models(DEMs)has made it possible to extract drainage network,calculate and store geomorphic parameters for hydrological modeling at different scales.Raster DEMs are the main data source used in hydrology.The effects of different grid cell sizes of raster DEMs on drainage basin characteristics were evaluated.Eight basins ranging approximately from10² km² to10⁴km² with elevations from129m to2618m in Xiaolangdi and Huayuankou section at the middle reaches of the Yellow River basin were examined in this study.Using DEMs with6different horizontal resolutions with grid cell sizes varying from100m to1000m,basin parameters included those commonly used in hydrology and geomorphology such as area,elevation,slope,channel length,drainage network are extracted and derived.According to the result,grid size affects the accuracy of derived drainage network,especially the case in the flat areas.Slope is more sensitive to the resolution of DEM than the area,the length and the shape is.Because of the different parameters derived from DEMs of different resolutions,the concentration time and lag time thus calculated vary more apparently in the same basin.