Abstract: The construction of the Three Gorges Dam and the South-to-North Water Diversion Project has significantly changed the hydrological situation in the middle reaches of the Yangtze River。From 2020 to 2022, the water resource from the Yangtze River and Han River decreased by 48.77%, 26.69%, 20.39% compared to 2018 in the Honghu River Basin, and the inflow of Xindi gate decreased by 87.32%, 23.00%, 67.61% from the Yangtze River. The dry-water situation is obvious in the middle reaches of the plain area, it showed the earlier dry season、longer dry season and lower dry season water level, resulting in the deterioration of water ecological environment in local areas. In this study, the Honghu watershed was taken as the research object, and we explored the phosphorus effect of large water-corridor construction in the plain lake area by SWAT model。The results show that: The SWAT model had a good applicability effect, the annual average phosphorus load is 744.90 tons from 2020 to 2022, and the results are close to those of numerous scientific research institutions, with a difference within 6%;the proportion of non-point source pollution is as high as 82%, which should be taken focus on the phosphorus pollution control in Honghu watershed; the construction of large water-corridor has a positive effect on improving the regional water eco-environment, it can effectively alleviate the water demand during the dry season by normalized water replenishment, and provide scientific evidence for "three-water coordinated" in region.