In order to better understand phosphorus (P) cycle in wetland ecosystem, the characteristics of phosphorus fractions in sediments of Heituwa constructed wetland system were investigated using soil organic phosphorus (Po) fractionation scheme and 31P-NMR technology. The concentrations of TP, Pi, Po and soil organic matter were all increased along the flow direction. Four kinds of P-compounds (orthophosphate, orthophosphate monoesters, orthophosphate diesters, and pyrophosphate) were detected in the NMR spectrum. Orthophosphate and phosphate monoester accounted for the dominants position in sediment phosphorus. This study indicates that the Po in sediment plays an importance role in wetland ecosystem and suggested that more attention should be paid to Po, especially to DNA-P and pyrophosphate in further research and management of constructed wetlands. Compared with the traditional chemical analysis method, 31P-NMR method has sample preparation relatively simple and is less destructive, with components analyzed completely. Using 31P-NMR technology, the cognition of wetland phosphorus cycle, especially organophosphate, will be expected to get new breakthrough.