The purpose of this study is to evaluate the stream flow and water quality (SS, T-N, and T-P) behavior of Nakdong river basin (23,609.3 km2) by simulating the dam and weir operation scenarios using SWAT (Soil and Water Assessment Tool). The operation senarios are the simultaneous release for all dam and weirs (scenario 1), simultaneous release for all weirs (scenario 2), and sequential release for the weirs with one month interval from upstream weirs (scenario 3). Before evaluation, the SWAT was calibrated and validated using 11 years (2005-2015) daily multi-purpose dam inflow at 5 locations (ADD, IHD, HCD, MKD, and MYD), multi-function weir inflow at 7 locations (SHW, GMW, CGW, GJW, DSW, HCW, and HAW), and monthly water quality monitoring data at 6 locations (AD-4, SJ-2, EG, HC, MK-4, and MG). For the two dam inflow and dam storage, the Nash-Sutcliffe efficiency (NSE) was 0.56~0.79, and the coefficient of determination (R2) was 0.68~0.90. For water quality, the R2 of SS, T-N, and T-P was 0.64~0.79, 0.51~0.74, and 0.53~0.72 respectively. For the three scenarios of dam and weir release combination suggested by the ministry of environment, the scenario 1 and 3 operations were improved the stream water quality (for T-N and T-P) within the 3 months since the time of release, but it showed the negative effect for 3 months after compared to scenario 2.