Carbon (C), nitrogen (N), and phosphorus (P) stoichiometry are critical indicators of biogeochemical coupling in ecosystems, and stoichiometric homoeostasis plays an important role in modulating the structure, function, and stability of ecosystems. Stoichiometry studies have been carried out in various terrestrial ecosystems in China, but little data is available for wetlands. Previous studies have largely focused on plant leaves. It is also important to assess the entire plant-soil system stoichiometry, rather than just plant tissues. Wetland plants live in a fluctuating environment, more so than terrestrial plants, and the responses of wetland ecosystems to climate change are more sensitive than terrestrial ecosystem. The C:N:P stoichiometry in wetlands and terrestrial ecosystems may differ. Thus, more research is needed on carbon, nitrogen, and phosphorus concentrations, as well as their stoichiometry in wetland ecosystems. Poyang Lake is the largest freshwater lake in China, with huge wetlands appearing during the drawdown periods each year. In this study, six dominant plant species, including Phragmites australi, Triarrhena lutarioriparia, Zizania latifolia (Griseb.) Stapf, Carex cinerascens, Carex argyi, and Polygonum hydropiper, were selected in the national nature reserve of the Nanji Wetlands of Poyang Lake. Fresh leaves, current year litter, and top layer soils were sampled and analyzed for carbon, nitrogen, and phosphorus. The objectives of this study were as follows:1) to clarify the difference between the carbon, nitrogen, and phosphorus concentrations of dominant plants, as well as their stoichiometric ratios; and 2) to discuss the vertical variability of carbon, nitrogen, and phosphorus stoichiometry among leaves, litter, and soils. Our results showed that carbon, nitrogen, and phosphorus ranged from 380.6 to 432.2, 15.3 to 32.6, and 1.3 to 2.0 mg/g in plant leaves, 345.4 to 416.1, 10.8 to 20.8, and 1.1 to 1.7 mg/g in litters, and 15.0 to 38.1, 1.2 to 3.1, and 0.7 to 1.1 mg/g in top soils, respectively. The elemental concentrations varied significantly with plant species and among leaves, litters, and top soils. Leaves had significantly higher levels of carbon, nitrogen, and phosphorus concentrations than litters and soil. Moreover, C:N, C:P, and N:P stoichiometry largely differed among plant leaves, litters, and soils, showing a clear vertical variation pattern; soil had the minimum ratios of C:N, C:P, and N:P. Soil C:N, C:P, and N:P stoichiometry was closer to that of litters, rather than plant leaves. Changes in the C:N ratio of litters could explain 35% of soil C:N ratio variability, whereas 18% of soil N:P ratio variability could be explained by litter N:P. In addition, a significant difference was found between emergent and hygromorphic plants for leaf N:P and C:N ratios, but not for leaf C:P ratio. In contrast, litter C:N, C:P, and N:P did not differ significantly between emergent and hygromorphic plants. Given the relatively low C:N and C:P ratio of plant litters, Poyang Lake wetlands may experience fast litter decomposition and turnover rates, leading to relative low carbon storage.