Abstract: The terrain analytic's basic theory for many fields and implement measure can be provided by digital terrain analysis based on DEM.As an important dimension parameter DEM grid resolution(horizontal resolution) plays a key role in determination of terrain parameters and application of scale.In this paper Gansu Loess Plateau region of the Malian River Basin was chosen as research object,utilizing the geography information system software which developed by American ESRI company,to have a drainage area's distill and analytic based on digital elevation model.The basic terrain characters of drainage area such as slope,aspect,and channel system,the demarcation of the small watershed was investigated.The effect of DEM horizontal accuracy toward character of terrain and hydrological have been concluded based on analyzing and comparing.