Ecological stoichiometry is a useful concept for studying the balance of multiple chemical elements in ecosystem interactions. In this study, we measured leaf and soil carbon (C), nitrogen (N), and phosphorus (P) levels in poplar plantation of three different stand ages (6-, 9-, and 13 year old), which were planted using the methods of digging furrows and lifting ridges, to explore the ecological stoichiometry characteristics and the distribution patterns of nutrient elements, and also to assess the ecological impacts of poplar plantations on Dongting Lake wetland ecosystem. The results showed that stand age had a significant effect on leaf N, P, C:P and N:P ratios, but not significantly correlated with leaf C and C:N ratio. For all three stand ages, the leaf N:P ratio was higher than 16, indicating that P is the main factor limiting the growth and development of poplar plantations in Dongting Lake wetland. The content of P in 9-year-old leaves was significantly lower than that in 6-year-old and 13-year-old leaves, whereas the ratios of C:P and N:P in 9 year-old leaves were significantly higher than those in 6-year-old and 13-year-old leaves, which showed that the limit of P had a particularly marked effect on 9 year-old poplar plantations. In both the ridge and furrow plots of the wetland poplar plantations, soil organic carbon (SOC), total N (TN) and C:N ratio were negatively correlated with stand age and depth of the soil layer. In contrast, total P (TP) was not significantly correlated with these two factors. The C:P ratio in the ridge plots was negatively correlated with stand age and soil depth, in the furrow plots, this ratio was positively correlated with the soil layers rather than stand age. For the N:P ratio, we detected a negative correlation with soil depth in the 9-year-old and 13-year-old ridge plots and in the 6-year-old furrow plots. These results illustrate that the ridge and furrow method used for planting poplars is detrimental to the accumulation of SOC and TN and to the maintenance of soil fertility in Dongting Lake wetland.