Abstract: Phosphorus is one of the limited factors for eutrophication of lakes.In order to understand the occurrence characteristics and release risks of phosphorus forms in sediment of the grass-type lakes, the phosphorus forms and release fluxes in sediments of Caohai Lake of Guizhou Province were analyzed by sequential extraction and pore water diffusion model.The results showed that the content of TP in Caohai Lake sediments was 563.75～982.40 mg/kg, and the average content was(722.97±71.38) mg/kg, which was a third-order pollution.TP has significant spatial differences, with higher TP content in areas with high human activity intensity.The rank of different phosphorus forms' content was NaOH-NRP > Res-P > NaOH-SRP > BD-P > HCl-P > NH4Cl-P.The active phosphorus(NaOH-NRP,BD-P and NH4Cl-P),which accounts for 58.05% of TP in sediments, was the main form of phosphorus in Caohai Lake.And the release fluxes were 0.03～0.08 mg/(m2·d).It indicated that the phosphorus in Caohai Lake spread from the sediment to the overlying water, showing as "source".In this study, we found that the proportion of organic phosphorus in Caohai Lake was relatively high, and the potential release risk was high.The phosphorus content and release flux in the sediments in Caohai Lake were lower than those of the algae-type lakes.The results have great significance for the conservation and management of the grass-type lakes.