Abstract: The objectives of this study were to investigate the changes in phosphorus in soils of Poyang Lake wetland under the combined action of soil water content and decomposition of Carex cinerascens through field sampling and laboratory simulation experimental analysis. The forms of phosphorus were analyzed by SMT and ³¹P-nuclear magnetic resonance spectroscopy (³¹P-NMR). The results show that the total phosphorus (TP) in soils of Poyang Lake wetland to be 531 mg·kg^-1 and the inorganic phosphorus (IP) to be 305 mg·kg^-1. The Ca-P was the main component of IP, and the organic phosphorus (OP) was 218 mg·kg^-1, which mainly consisted of monoesters, diesters, and pyrophosphate. Affected by different soil water contents (dew dry, humidity, wet dry, rising water levels, and falling water levels), the changes of TP, IP, and Ca-P in 0-2 cm surface soils were similar and showed varying degrees of decline, and the maximum decrease was observed in the wet dry group. The changes in Fe/Al-P in the 0-2 cm wet dry group were similar to those in the dew dry group, which were lower than those of other culture groups; the content of OP in 0-2 cm soils did not change significantly with different culture groups. Under the decomposition of plants and soil water content, the content of TP, IP, OP, diester/monoester, and diester/pyrophosphate were significantly increased in >2-5 cm soil. However, the contents of TP, Fe/Al-P, and OP in 0-2 cm soil were significantly lower, and the decrease amplitude of OP (9.0%-15.2%) was much higher in other groups under the single factor of soil water content, indicating that the decomposition of plants increased the activity of soil microorganisms and increased the decomposition rate of OP in topsoil.