[Objective] This study aims to quantitatively evaluate the effects of the emergency regulation of the Three Gorges Reservoir in response to the Tuanzhou polder breach emergency, thereby improving the understanding of flood control regulation of the Three Gorges Reservoir and laying a foundation for further optimization of its operation in the future. [Methods] A one-dimensional and two-dimensional coupled hydrodynamic model for the Jingjiang River reach and east Dongting Lake was established and validated with field-measured data. Hydrological conditions of the river-lake system under different regulation scenarios of the Three Gorges Reservoir were designed and simulated, and the effects of reservoir regulation on river-lake discharge and water levels were quantitatively analyzed. The development of emergencies in the Dongting Lake area (including Tuanzhou polder) before and after the breach, as well as the variation of water level at Qilishan, were analyzed. The effects of the Three Gorges Reservoir regulation on alleviating the flood-control pressure in the Dongting Lake area were discussed. [Results] Compared with the original regulation plan before the Tuanzhou polder emergency, the actual regulation of the Three Gorges Reservoir reduced the water level in east Dongting Lake by up to approximately 0.34 m, and advanced the time for the water level at Qilishan station to fall below the warning level by 18 hours. Flood-control emergencies in the Dongting Lake area mainly occurred during the high-water period after the water level exceeded the warning level and during the water recession period, and the regulation of the Three Gorges Reservoir reduced the probability of emergencies in the Dongting Lake area. [Conclusion] The emergency regulation of the Three Gorges Reservoir shortens the duration of the Qilishan water level exceeding the warning level and alleviates flood-control pressure in the Dongting Lake area. This study provides a scientific and quantitative evaluation of the regulation effects of the Three Gorges Reservoir, which provides a basis for further optimization of its operation.