Abstract: Litter decomposition is a key process of carbon and nutrient cycling in wetland ecosystems. Comparing the decomposition rate of leaf litter and fine roots is helpful to clarify the relative contribution of different litter types to wetland carbon cycle under the condition of water change, and improve our understanding of the decomposition driving mechanism of different organic carbon sources. The decomposition dynamics of leaf and fine root litters of Carex thunbergii, a typical wetland plant in the Shengjin Lake Wetland, Anhui Province, were studied using the litterbag method under different simulated soil water contents. The results showed: (1) After 5 months of decomposition, under soil moisture content of 30%, 50% and 70%, the mass remaining for fine roots of C. thunbergii was 46.7%, 58.1% and 60.1%, and the mass remaining for leaf litter was 37.9%, 31.6% and 33.9%, respectively. (2) Under soil water content of 30%, 50% and 70%, the decomposition rate constants for fine roots were 1.78, 1.27 and 1.12, respectively, and for leaf litter were 2.56, 2.94 and 2.54, respectively, and there were significant differences between various soil water contents (P < 0.05). (3) The mass loss of fine roots was negatively correlated with soil water content (P < 0.001), and the positively correlated with leaf litter (P=0.01). (4) The results of repeated-measures ANOVA show that the decomposition of litters was affected by the litter type, decomposition time and their interaction, with litter type being the dominant factor. When analyzing fine roots and leaf litter separately, soil moisture content significantly affected the decomposition of fine roots, while the decomposition process of leaf litters was mainly influenced by retrieval time. Overall, the decomposition rate of leaf litter was faster than that of fine roots under the same soil moisture content. Soil moisture content differentiated the decomposition of fine roots and leaf litter in a wetland ecosystem with fluctuating groundwater table. The increase of soil water content promotes the decomposition of leaf litter, but suppresses the decomposition of fine roots.