The effect of simulated N deposition on forest ecology systems is a hot topic in global change ecology research. Soil C storage is sensitive to atmospheric N deposition, which helps to increase the exogenous N content in litter decomposition process and indirectly affects chemical process and the decomposition rate of litter decomposition. Therefore, it is of great importance to understand the relationship between litter decomposition and soil C and N in response to N deposition in order to accurately predict ecosystem C sequestration. In this study, we surveyed the relationship between leaf litter decomposition and soil C and N stoichiometry in different-aged P. massioniana stands in the Three Gorges Reservoir Region using an situ litter bag method. Four levels of simulated N content were implemented:control (CK, 0 g m^-2 a^-1), low N (LN, 5 g m^-2 a^-1), medium N (MN, 10 g m^-2 a^-1), and high N (HN, 15 g m^-2 a^-1). The results showed that simulated N deposition accelerated leaf litter decomposition in 20- and 30-year-old stands. In 46-year-old stands, however, only the litter in the LN treatment accelerated decomposition over 540 days of decomposition. The leaf litter decomposition rate was the highest in the 30-year-old stands for all four treatments, showing that leaf litter with lower initial N content from the same specie presented positively response to simulated N deposition. Specifically, N deposition promoted the decomposition of leaf litter with lower initial N content, while the decomposition of leaf litter with higher initial N content easily reached nitrogen saturation. Nitrogen deposition inhibited the litter carbon release from the litter in 20- and 46-year-old stands (0.62%-6.69% lower than the control), while it promoted carbon release in 30-year-old stands (0.28%-5.55% higher than in the control). The amount of immobilized N was 0.15%-21.34% higher in the leaf litter of the N deposition treatments than in that of the control for 30- and 46-year-old stands, while it was 5.70%-13.87% lower than in the control for 20-year-old stands. This indicates that simulated N deposition accelerated C release from the litter with lower initial C content and N immobilization of the litter with lower initial N content. Soil organic carbon increased in 30-year-old stands under simulated N deposition when compared to the control and was positively correlated with leaf litter C and N content and decomposition rate, while it was negatively correlated with the C/N ratio. Soil total nitrogen was positively correlated with the leaf litter decomposition rate and leaf litter N content, and the ratio of soil organic carbon to total nitrogen was positively correlated with leaf litter C and N content. In the control, the effect of leaf litter N content on soil nutrients was most significant, litter C:N ratio and C content followed, litter leaf decomposition rate was least, while in LN, MN and HN treatments, the effect of leaf litter C:N ratio on soil nutrients was most significant, litter N content and leaf litter decomposition rate followed, litter C content was least. In this study, P. massinonana stands with a low concentration of soil nutrients responded positively to N deposition, which accelerated leaf litter decomposition and improved soil fertility. These results suggest that soil carbon in ecosystems with low-quality leaf litter and a low concentration of soil nutrients would respond more to N amendment than it would in other ecosystems.