Flood disaster is one of the major natural disasters, the frequency and destructive power of it ranks one of the top disasters in China. In the flood risk assessment, the distribution of drainage network is a very important assessment factor. This study extract the watershed features of Pearl River Basin and Luan River Basin based on the Digital Elevation Model (DEM) and GIS-supported geospatial data model (Arc Hydro). Developed by the Hydrological module in ArcGIS, Arc Hydro is a hydrologic data modeling tool for the application of water resource. This paper aims to provide reliable data for the analysis of risk assessment and level of flood disaster by extracting drainage network using Arc Hydro. The study results showed that, it is feasible and effective to extract the risk assessment factors-drainage network based on DEM and Arc Hydro.