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 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 and Fe (DGT P and Fe) and dissolved P and Fe in WLFZ’s soils after inundation. The results showed that the average concentrations of DGT P and Fe, dissolved P and Fe were 0.022, 0.050, 0.151 and 1.515 mg/L, respectively. The peaks of dissolved P and Fe at both 150 m and 160 m elevations and DGT P and Fe at 150 m elevation occurred in the middle and deep layers, while the peaks of DGT P and Fe at 160 m elevation occurred at the soil-water interface. Following flooding, phosphate release at 150 m was mostly driven by the reduction of Fe oxides, which increased P concentration 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 elevation. The capacity of available solid P pool to replenish solute P in pore water were 0.291 and 0.286, which was in the medium level at 150 and 160 m elevations, respectively. The average diffusion fluxes of P at the soil-water interface at 150 m and 160 m elevations were 5.60×10^-6 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. In conclusion, the current risk of soil P release after inundation in the tributary’s bay WLFZ in the Three Gorges Reservoir is notably low, which is related to the input of P in the overlying water.