Abstract: The adsorption and desorption process of phosphorus (P) at the sediment-water interface plays a significant role in the eutrophication. At present, the adsorption desorption characteristics of P from subtropical bay sediments to the overlying water, and the effects of sediment size composition and physicochemical properties on P adsorption and desorption in sediments are not clear. Surface sediments were collected from three main estuarine regions of a subtropical bay for global germplasm resources (Crassostrearivularis Crould) reserve, to study P adsorption desorption characteristics of sediments to overlying water through adsorption kinetics and isothermal adsorption experiments, and constrain the effects of environmental factors such as sediment particle sizes, pH and salinity on sedimentary P adsorption and desorption. Chemical speciation of P in sediments before and after adsorption experiments was quantified using a sequential extraction (SEDEX) method, and the binding mechanisms of P in sediments were explored. The results showed that the adsorption kinetics process of P in sediments could be described by a pseudo-second order kinetic model, and the isothermal adsorption curves fitted the modified Langmuir-crossover model. The maximum adsorption capacity (Q_m) of P in sediments and the adsorption/desorption equilibrium mass concentrations (EPC₀) of P ranged from 0.332 to 0.864 mg/g and 0.076 to 0.150 mg/L, respectively. Surface sediments with smaller particle sizes had a high adsorption capacity of P. Seawater pH and salinity in estuarine regions of the subtropical bay were conducive for P adsorption in sediments. The contents of exchangeable P (Ex-P) and iron-bound P (Fe-P) increased significantly in different sediment samples after adsorption. The adsorption processes of P in sediments involved physical and chemical adsorptions. This study reveals that higher contents of clay minerals and high molecular weight organic matter promoted the adsorption of P in sediments of the subtropical bay, the pH and salinity of seawater have a certain buffer effect on water eutrophication in this region, but physical adsorption and binding capacity of P in sediments of the subtropical bay are weak, and there may be a risk of P re-release. Therefore, more attention should be paid to endogenous P pollution in the area, which is very important for preventing and controlling eutrophication in the subtropical bay.