Five dominant herbaceous species, Cynodon dactylon, Hemarthriaaltissima, Echinochloacrusgalli, Setariaviridis and Digitariasanguinalis, in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) were investigated. In order to determine how total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) are released while the plants are submerged in water, the stems and leaves of these plants were collected and submerged in water for 60 days in a laboratory. The results showed that the decomposition of the soaked plants caused a decrease in pH of the water. The maximum unit cumulative release amounts of TOC, TN and TP were 21.03-43.65, 0.50-3.23 and 0.54-2.69 mg/g, respectively, which occurred between the 15thand 20thdays. Furthermore, the maximum unit cumulative release rates of the plants varied significantly. Microbial activity, temperature and concentration of overlying water impacted the release of TOC, TN and TP. Based on previous reports on the vegetation of WLFZ and the maximum unit cumulative release amounts, the release amounts of TOC, TN and TP in the WLFZ during the impounding period of TGR were estimated. It was estimated that large amounts of TOC, TN and TP could be released within the 20 days during impoundment, which could result in a deterioration of local water quality and have an impact on water environment security during the initial period of impoundment.