The water volume and total phosphorus data of Taihu Lake from 2000 to 2020 were collected and sorted out. The the Taihu Lake Basin flood in 2020 and the change trend of total phosphorus pollution in Taihu Lake thereafter were analyzed and compared with the flood in 2016. The characteristics of flood, phosphorus flux in and out of the lake, phosphorus concentration in rivers around the lake, phosphorus stock and composition of Taihu Lake were studied, and the impact of the flood in 2020 on total phosphorus pollution in Taihu Lake was clarified. The results show that the flood in 2020 did not cause the rebound of total phosphorus pollution in Taihu Lake, and the total phosphorus pollution in Taihu Lake improved significantly after 2020. Unlike the flood in 2016, the flood in 2020 did not cause an increase in lake-inlet phosphorus flux. The total phosphorus mass concentration entering the lake in 2020 has decreased by 21.5% compared to the average value since 2007, which is the main reason why the phosphorus flux into the lake has not increased.