This study intends to estimate the best model parameters for predicting the water quality and discharge of the study area, and provide the basic data necessary for predicting the water quality and discharge and examining changes in water quality on the basis of the changes hydraulic and hydrological changes and pollutional load of the study area. Nakdong River was selected for analysis, and the water quality survey data necessary for parameter estimation was based on the monthly water quality data (discharge, BOD, T-N and T-P) between December 1, 2002 ${sim}$ November 31, 2002. The topographical characteristics factors of the study area were based on the 1/25,000 numerical map published by the National Geographic Information Institute and satellite photographs. The presumed course: It measured the most suitable parameter that could imitate surveyed water quality and discharge using the method of trial and error, in this part the first numerical value was the model parameter presented SWAT. The result of analisys showed that a relative error between surveyed value and the result of water quality imitation about BOD, T-N, T-P that examined by this study, discharge correction: $R^2=0.912$, discharge verification: $R^2=0.838$, correction and verification of BOD: $R^2=0.847$, correction and verification of T-N : $R^2=0.712$ and, correction and verification of T-P : $R^2=0.726$ and, BOD: RK1, RK3, T-N : RS3, RS4, T-P : RS2, RS5, GWSOLP, discharge : ALPAHA_BF, GWQMN, CH_N(2), CN2, SOL_AWC have been considered as the factors of the water quality performed in this water quality simulation, that is, the most effective parameters on BOD, T-N and T-P. It is considered that it will be possible to apply the most optimal parameter to an analysis of the water quality and discharge simulation at study area in the goal year by examining the interaction of the parameters through the parameters sampling which are able to applicable to prediction of the water quality and discharge in the future, also the analysis on the basis of the hydrological conditions: an outflow or the character of a flow will be needed.