【Objective】While the Three Gorges Reservoir (TGR) plays a crucial role in mitigating extreme droughts in the middle and lower Yangtze River basin, quantitative assessments of its drought-relief water supplementation effects remain insufficient. This study aims to quantitatively analyze the regulatory effects of the Three Gorges Reservoir’s water supplementation on water levels and discharge in the mainstem of the middle and lower reaches, providing theoretical basis for scientific evaluation of drought mitigation benefits.【Method】Utilizing daily water level and discharge data from the TGR and the middle-lower Yangtze River between 2020 and 2022, a one-dimensional hydrodynamic model was employed to analyze the water replenishment effects of the TGR on the downstream reaches.【Result】(1)Model validation confirmed high simulation accuracy for all study sections, demonstrating its reliability for drought mitigation studies. (2) Water supplementation analysis revealed that maximum water level increases in the Shashi-Hankou reach, with progressive downstream attenuation. When the TGR maintained a discharge of 5 000 m³/s with a supplementation flow of 3 000 m³/s, the Shashi station showed increases of 2 018 m³/s in discharge and 1.03 m in water level. These effects decreased to 895 m³/s and 0.40 m at Hankou station, further declined to 645 m³/s and 0.34 m, 536 m³/s and 0.16 m at Jiujiang and Datong stations, respectively. (3) During August and September 2022, two drought-relief water supplementation operations released 830 million m³ and 680 million m³ of water, respectively. The Shashi-Hankou reach benefited substantially: in the second operation, Shashi station received a cumulative supplementation of 642 million m³, delaying water cutoff at Shishou waterworks by 6 days, while Luoshan station received 574 million m³, postponing Panwan waterworks’ cutoff by 5 days. Downstream of Hankou, flow augmentation predominated, with Datong station accumulating 300 million to 400 million m³ of supplemented water, crucial for maintaining its 10 000 m³/s minimum ecological flow threshold.【Conclusion】The drought-mitigation water supplementation operations from the TGR significantly alleviated drought conditions in the middle and lower reaches. We propose implementing differentiated regulation strategies. water-level-oriented regulation for the Shashi-Hankou reach, and discharge-focused control for downstream sections (with particular emphasis on maintaining the minimum ecological flow threshold of 10 000 m³/s at Datong station). These strategies should be complemented by section-specific water supplementation schemes tailored to the temporal water demand variations at different cross-sections, thereby optimizing the overall ecological benefits of water supplementation.