To explore traits related to leaf decomposition and the potential contribution of the phosphorus of the leaves of Taxodium distichum to the soil-water system in the fluctuation zone of the Three Gorges Reservoir, an indoor experiment was conducted upon simulation of the water change of the hydro-fluctuation belt in the reservoir. Five different kinds of water treatments were applied to investigate leaf decomposition processes of T. distichum and phosphorus release characteristics. Five water treatments included normal growth water condition (CK), light drought water stress (T1), water saturation (T2), 2 cm flooding (T3), and 10 cm flooding (T4). The results showed that:1) During the entire experiment period (90 d), the rate of leaf weight loss of the two flooding groups reached 51% (T3) and 55% (T4), which were significantly higher than that of the three unflooded treatment groups of CK, T1, and T2; 2) The total phosphorus content in leaves increased in the CK, T1, and T2 treatment groups, but decreased in the flooding treatments (T3 and T4); 3) The total phosphorus content of the soil showed fluctuation characteristics during the experiment period, but at the end of experiment there was no significant difference in soil total phosphorus content between the treatment groups and the CK group; 4) During the experiment period, total phosphorus content of the overlying water of the T3 and T4 treatment groups with addition of leaves increased significantly compared with that of the respective treatment groups without addition of leaves and showed a rapid increase in the initial decomposition rate followed by a gradual decrease and finally a stable state. The peak value of leaf decomposition was observed on the 10^th day, after which leaf decomposition decreased. However, at end of the experiment the total phosphorus content of T3 and T4 treatment groups with addition of leaves was still significantly higher than that of the respective treatment groups without addition of leaves, reaching 17.15 (T3) and 5.81 (T4) times higher, respectively. These results indicated that:water flooding can promote the decomposition of the leaves of the T. distichum; the decomposition of leaves under different water conditions did not significantly affect the phosphorus content in the soil; and the decomposition of the leaves of the T. distichum during flooding may increase the phosphorus content in the water. Therefore, it is necessary to collect the leaves of the T. distichum in the hydro-fluctuation belt in a timely manner in order to reduce the phosphorus load of the water body in the reservoir area as much as possible.