HSPF model based on BASINS was applied to analyze effects of watershed management measures for water quality conservation in the Hwaseong Reservoir watershed. The model was calibratcd against the field measurements of meteorological data streamflow and water qualities (BOD_5 T-N T-P) at each observatory for 4years (2007-2010). The water quality characteristics of inflow streams were evaluated. The 4 scenarios for the water quality improvement were applied to inflow streams and critical area from water pollution based on previous researches. The reduction efficiency of point and non-point sources in inflow streams was evaluated with each scenario. The results demonstrate that the expansion of advanced treatment system within wastewater treatment plants and construction of pond-wetlands would be great effective management measures. In order to satisfactory the target water quality of reservoir the measures which can control both point source and non-point source pollutants should be implemented in the watershed.