Abstract: The water quality is significantly influenced by the hydrological processes of the watershed． Constructing a water quality model coupled with watershed hydrological processes can improve simulation accuracy and management effectiveness． This study, based on raster-based runoff algorithms, intelligent optimization algorithms, and unified spatiotemporal resolution technology, develops a scale transformation and flux coupling optimization algorithm for nitrogen and phosphorus pollutants within the full watershed hydrological source-flow-sink chain． By utilizing a three-dimensional water quality equation and the Manning formula, a loose coupling of watershed runoff capacity and water quality response is achieved． Ultimately, a water quality response model coupled with watershed source-flow-sink hydrological processes is developed and successfully applied to a certain river basin in northern China． Results show that the model’s hydrological and water quality simulation coefficients exceeded 0.9 and 0.6, respectively, indicating high accuracy and good applicability． This model provides technical support for the study of watershed source responses in regions with limited monitoring data, and offers decision-making support for lake water quality management．