The main objective of this study is to simulate design flood discharge of the Sungjoo basin. GIS and HEC-HMS were used in this study. GIS technique can extract various hydrological factors from D.E.M(Digital Elevation Model) and the parameters extracted from each watershed were applied to the HEC-HMS. As a result of this study, GIS technique is useful to the extraction of watershed characteristics factors and HEC-HMS is successful in the simulation of design flood discharge.