Abstract: Soil phosphorus (P) can be transformed into various forms during the continuous dry-wet cycles, which is a critical process of soil P release in the riparian zone of the Three Gorges Reservoir. Therefore, the purple alluvial soils were collected and incubated under the drying and flooding conditions to explore the transformation processes and rates of soil P forms in the riparian zone of the Three Gorges Reservoir. The soil P forms were analyzed using the modified Hedley phosphorus sequential fractionation method. During the drying period, the transformation rates of soil sodium hydrogen carbonate extraction organic P (NaHCO₃-Po) and sodium hydrate extraction inorganic P (NaOH-Pi) increased from -6.27, -1.78 mg/(kg·d) to -0.69, -0.21 mg/(kg·d), respectively, and the proportions of NaHCO₃-Po and NaOH-Pi content in ex-Residual-P decreased by 21.58% and 5.95%, respectively. Contrarily, the transformation rates of soil water-soluble P (H₂O-Pi) and sodium hydrogen carbonate extraction inorganic P (NaHCO₃-Pi) decreased from 2.07, 1.74 mg/(kg·d) to 0.43, 0.42 mg/(kg·d), respectively, and the proportions of H₂O-Pi and NaHCO₃-Pi content in ex-Residual-P increased by 13.50% and 13.41%, respectively. During the flooding period, the transformation rates of NaHCO₃-Pi, NaHCO₃-Po and soil sodium hydrate extraction organic P (NaOH-Po) increased from -1.84, -4.98 and -1.72 mg/(kg·d) to -0.26, -0.55 and -0.12 mg/(kg·d), respectively, and the proportions of NaHCO₃-Pi, NaHCO₃-Po and NaOH-Po content in ex-Residual-P decreased by 9.12%, 19.33% and 4.03%, respectively. However, the transformation rates of H₂O-Pi, NaOH-Pi and soil hydrochloric acid extraction P (HCl-Pi) decreased from 4.51, 2.00 and 0.47 mg/(kg·d) to 0.63, 0.22 and 0.05 mg/(kg·d), respectively, and the proportions of H₂O-Pi, NaOH-Pi and HCl-Pi content in ex-Residual-P increased by 28.83%, 2.46% and 1.18%, respectively. In conclusion, NaHCO₃-Po and NaOH-Pi tended to be transformed into H₂O-Pi and NaHCO₃-Pi during the drying period, while NaHCO₃-Pi, NaHCO₃-Po and NaOH-Po were mostly transformed into H₂O-Pi, NaOH-Pi and HCl-Pi during the flooding period. NaHCO₃-Po was the main source of H₂O-Pi in the riparian zone during both the drying and flooding periods. Therefore, under the conditions of rainwater leaching and flooding, the release of P from soil in the riparian zone to the Three Gorges Reservoir can be decreased effectively by NaHCO₃-Po reduction.