The process of phosphorus (P) exchange at soil-water interface remains unclear following flooding in the Three Gorges Reservoir’s Water-Level Fluctuation Zone (WLFZ), which could lead to an increase in the P load in the water. In this study, Diffusion Gradients in the Films (DGT) and High-resolution dialysis (HR-Peeper) were employed to simultaneously measure DGT labile P/Fe (DGT-P/Fe) and dissolved P/Fe in WLFZ’s soils after inundation. The results showed that the average concentrations of DGT-P, DGT-Fe, dissolved P and dissolved Fe were 0.022 mg/L, 0.05 mg/L, 0.151 mg/L and 1.0515 mg/L, respectively. The peaks of dissolved P and dissolved Fe at both elevations and DGT-P/Fe at 150m elevation occurred in the middle and deep layers, while the peaks of DGT-P/Fe at 160m elevation occurred at the soil-water interface. Following flooding, phosphate release at 150 m was mostly driven by the reduction of Fe oxides, which leading increase in concentration of P in the water. However, plant root limitation, soil heterogeneous structure, and overlaying water P infiltration stress all had an impact on P diffusion at 160 m. The capacity of the available solid P pool to replenish solute P in pore water were 0.291、0.286, which was in the medium level at 150 and 160 m, respectively. The average diffusion fluxes of P at the soil-water interface at 150 m and 160 m were 5.60×10-6 mg/cm2/d and -5.68×10-6 mg/cm2/d, respectively (positive values indicate the release of P from the soil), which were significantly lower than the results of sediments in previous studies. Therefore, the current risk of soil P release after inundation in the tributary’s bay WLFZ in the TGR is notably low, which was related to the input of P in the overlying water.