Abstract: Xiangxi River has always been confronted with the issue of eutrophication.To ascertain the distribution of phosphorus over the river basin, a SMT chemical extraction technique was employed to assess the spatial distribution of various phosphorus forms, and the correlation between phosphorus and phytoplankton was discussed.The findings reveal that the total phosphorus (TP) concentration in the water varied from 0.137 to 0.997 mg/L, with a mean value of 0.444 mg/L, and particulate phosphorus (PP) was the predominant form of phosphorus present in the waters.In sediments, the total phosphorus (TP) concentration ranged from 427.25 to 2 619.43 mg/kg, averaging 992.91 mg/kg, with calcium-bound phosphorus (Ca-P) the most abundant form.Moreover, the bioavailable phosphorus (BAP) content oscillated between 264.97 and 366.75 mg/kg.Notably, the surface BAP content was 25.37% higher than the average BAP content, indicating a high risk of phosphorus release.The algal cell density in the water ranged from 5.19×10⁵ to 7.02×10⁷ cells/L, exhibiting a highly significant correlation with the dissolved phosphate (SRP) content in the water body.The Pearson correlation coefficient between algal cell density and SRP was 0.958.These findings offer valuable data for the scientific management and preservation of the Xiangxi River′s aquatic environment.