Litter decomposition is an important ecological process for maintaining energy flow, material cycling and nutrient balance in wetland ecosystems. From November 2017 to April 2018, a field decomposition experiment was conducted in the Lake Poyang wetland. The decomposition process and δ¹³C, δ¹⁵N differentiation characteristics of cellulose and lignin in the litter of three dominant plants, Phragmites australis, Triarrhena lutarioriparia and Carex cinerascens, were investigated using the decomposition bag method. The results showed that there were significant differences in cellulose and lignin residues, decomposition rate and δ¹³C, δ¹⁵N among the three plant litter types during the 150 d experiment. The main cause of these differences was attributed to the initial chemical properties of the different plant litter types, especially differences in C/N and lignin/N. The decomposition rate of litter cellulose and lignin was fastest in P. australis, followed by C. cinerascens and T. lutarioriparia. The decomposition process of the three plant litters was simulated and predicted using the Olson negative exponential decay model. During the decomposition of the three plant litters, δ¹⁵C fluctuated continuously but showed an overall significant decreasing trend, while δ¹⁵N for all litter types showed a slightly increasing trend in volatility, indicating that it was influenced by both substrate quality and microbial metabolic activities at different stages of decomposition. There was a significant positive correlation between δ¹³C and the decomposition rate of cellulose and lignin in the litter. However, the correlation between δ¹⁵N and the decomposition rate was not significant, indicating that there are other factors besides the migration and transformation of nitrogen elements that affect the change in δ¹⁵N. This study can contribute to a better scientific understanding of the substrate quality control mechanism in the process of litter decomposition, and provide a scientific basis for the protection and restoration of Lake Poyang wetland.