Fire is a common disturbance both from natural source and anthropogenic activities and an important factor in driving the variation of soil organic carbons. A 5-year study was conducted to examine the influence of annual prescribed fire on soil organic carbon (SOC) fraction in a fire-prone plant community, Triarrhena lutarioriparia community, in Poyang Lake, China. The results showed that after burning the contents of dissolved organic carbon (DOC), soil microbial biomass carbon (SMBC) and light fraction organic carbon (LFOC) increased significantly from 78.53 mg/kg to 131.72 mg/kg, 365.58 mg/kg to 603.42 mg/kg, and 14.82 g/kg to 20.56 g/kg, respectively, during the 5-year studying period. On the other hand, the contents of total SOC and heavy fraction organic carbon (HFOC) only increased slightly from 53.67 g/kg to 61.39 g/kg and 33.45 g/kg to 37.46 g/kg, respectively. The results strongly suggested that DOC was more sensitive to the prescribed fire than SOC. Moreover, the annual ratios of DOC, SMBC and LFOC to SOC significantly increased after burn treatments. Taken together, prescribed fire could greatly increase the contents of soil active organic carbons, and enhance the carbon cycle in Poyang Lake. Thus, it could be taken as an exercisable measure to improve the carbon capacity and maintain the soil productivity in the lake wetland.