In this paper

the authors present a technique of watershed structure extraction and watershed partition automatically based on gird digitial elevation model（DEM） data . This technique consists of three parts:definition of topographic structure; topographic structure; definition of watershed structure; and algorithm design which is used to extract the characteristics of topography from DEM data. The authors consider that the channel network and the divided network as the two basic frameworks of a watershed. The polygons constructed by the above networks are corresponding to the catchments which make up the watershed. The framework consisting of these catchments

the basic topographic units

and their topologic relationship can be used to store the watershed information and to construct spatial distributed mechanism-course models. The watershed of Wangjiagou in Lishi Gounty of Shanxi Province

located in a gully area in loess plateau

was selected as a pilot study area

and the final results are in accordance with the real condition of the case study area.