Regional nutrient management model was developed based on original generalized watershed loading functions (GWLF) to implement a case study in the drinking water sources of Tianjin City. The main environmental actions of SHR watershed were estimated, including the simulations of streamflow and dissolved nitrogen (DN) load fluxes in monthly scale, as well as the analyses of DN pollution source apportionment. The modeling result could meet the requirements in management with a reliable modeling accuracy, which is valuable for demonstrating in referenced area.