Abstract: The total phosphorus (TP) flux from the Changjiang River Estuary into the sea significantly affects the water environment and aquatic ecology of the nearshore areas.Based on an optimized control section at the river-sea interface, TP concentrations in the estuary waters and TP flux into the sea from 1999 to 2022 were investigated.The results showed that: ① Since 1999, the annual TP flux into the sea has exhibited substantial interannual fluctuations, with the maximum annual flux being 6.3 times of the minimum.Particulate phosphorus flux varied more markedly than dissolved phosphorus flux.② TP concentration and flux generally followed a pattern of first increasing and then decreasing.The turning point occurred in 2010, when the annual average TP concentration at the control section reached 0.470 mg/L, and the TP flux into the sea peaked at 455, 700 tons.Between 2008 and 2012, TP flux into the sea remained relatively high, averaging 290, 500 tons per year.From 2018 to 2022, it declined to an average of 143, 300 tons per year, indicating significant effectiveness of phosphorus pollution control in the Changjiang River Basin.③ Since 2010, both the TP flux and particulate phosphorus flux into the sea, as well as their relative proportions, have shown a pronounced decreasing trend.The proportion of particulate phosphorus dropped from 90% in 2010 to 43% in 2022.④ TP concentrations in the Changjiang River Estuary are higher in the dry season than in the wet season, whereas TP flux into the sea is greater in the wet season than in the dry season.⑤ From 2018 to 2022, phosphorus contributions from the upper reaches of the Yangtze River, Dongting Lake, Hanjiang River, and Poyang Lake accounted for 30.5%, 12.0%, 4.5%, and 5.9%, respectively, while other sources contributed 44.0%.