Based on the 30×30m DEM and GIS, taking an example of the Fenghuoshan Basin in Qinghai-Xizang Plateau, the paper discusses watershed hydrological modeling and designs the scenario and algorithm of the hydrological response unit(HRU)division with finite volume method of irregular grid. Sub-basins are generated from DEM data, and types of soil cover can be devided by remote sensing images. Every hydrological unit has a uniform type soil cover, threshold value of catchment area is calculated based on the chart to get the threshold of watershed area catchment area. Combined with the irregular grid of finite volume method, the paper discusses the watershed grid division, and then defines decoding method of the differential equation. The results show that combining RS with GIS can accuratly divise the land use type of watershed and get the threshold of watershed catchment area. Spatial discretization of distributed hydrological model is realized by divising wathershed grid unit and storing grid data. It''s practicable and workable to apply this method to numerical simulation of permafrost meadow area.