The basic theory of R-V GIUH is introduced.Due to a lot of data of precipitation and runoff are needed when determining a basin's unit hydrograph,the method of applying Geographic Information System(GIS)to establish basin's Digital Elevation Model(DEM)is presented.The unit hydrograph can be determined only on the basis of topographic date to resolve the problem of the flood forecasting in the data shortage region.The method is applied in Yanduhe River Basin of Three Gorges Interval of Yangtze River and the results are satisfactory.