The variation of inflow and outflow total phosphorus (TP) loads is a key factor that affects the state of eutrophication in Poyang Lake. Based on the monitoring data of water quality and quantity from 2009 to 2018, the inflow and outflow TP loads around Poyang Lake were calculated, the arithmetic mean and the weighted mean of annual TP concentrations were attained, and their spatio-temporal variations were analyzed. Moreover, the relations of inflow water volume and TP concentration versus inflow TP load were examined by using double accumulation curve method and regression analysis method to reveal the dominant factors for pollution loads. Findings revealed: (1) Compared to arithmetic mean, the weighted mean concentration of TP better reflects the spatio-temporal difference of water quality and volume around Poyang Lake. Annual inflow TP concentration in Raohe River stood at the highest (0.123 mg/L), followed by Xinjiang River (0.091 mg/L), Fuhe River(0.069 mg/L), Ganjiang River (0.063 mg/L), and Xiushui River (0.045 mg/L). (2) Annual inflow TP load totaled 98 514 t, lower than outflow (108 442 t), omitting inputs from waterfront, sediment release, and dry-wet subsidence. (3) Ganjiang River(45 208 t) and Raohe River (19 320 t) were top two contributors to the total inflow TP load among the five rivers, of which Ganjiang River alone accounted for 46%. (4) Significant correlations were found between monthly inflow TP load and inflow water quantity across different water zones, indicating that TP loads are largely influenced by inflow water volume.