Abstract: Digital twin technology, as an innovative advancement in recent years, achieves high-precision mapping of the real physical world by constructing accurate virtual models.This provides a new perspective and approach to addressing the issues in traditional water quality safety management.Water quality models are central to realizing precise mapping and virtual-real interaction of water quality in digital twin lakes and reservoirs.To address the water quality safety management needs of Danjiangkou Reservoir, the source of the Middle Route of the South-to-North Water Diversion Project, a novel three-dimensional hydrodynamic water quality model was proposed.This model overcame various technical challenges of traditional models, including simulation distortion, error accumulation, slow computing speed, and the inability to meet decision-making requirements for sudden pollution events.The model was calibrated using in-situ flow field observations and water quality monitoring data.Results demonstrated that the model significantly enhances computational efficiency and simulation accuracy through key technologies such as combinedσ/zgrid, total phosphorus constitutive equation, simulation of sudden pollution treatment, OpenMP parallel computing, hydrodynamic pre-computation, dual time-step mode, and pollution plume diffusion trajectory tracing.Practical application during the Hanjiang River autumn flood in 2023 proves the model′s effectiveness in supporting the "four-pre" functions of water quality safety(forecast, pre-warning, rehearsal, and pre-emergency planning).The simulation results provide crucial technical support for flood prevention and post-flood water quality safety assurance in the Hanjiang River.