The watershed topography is a key factor for extraction of the drainage

and it is also a very important topic in the study of digital watershed and the distributed hydrological models.The paper firstly discusses some problems in hydrological analysis by applying the DEM

and describes three kinds of interpolation models to produce the DEM.Then the author introduces an interpolation method which could improve the accuracy of the DEM by judging the stream's flow direction.Finally the interpolation algorithm is applied to generate the DEM by using the elevation and stream data in the area of southwest China.We analyze the results of the experiment

and find that the DEM created by this method not only keeps its precision but also presents a fine surface runoff character and stream pattern.Moreover

by comparing with the stream lines that extracted from different DEMs

the paper concludes that the DEM created by the hydrological improved algorithm is more useful in dealing with the hydrological analysis.