To understand the carbon density and environmental factors in Dongting Lake wetland, 24 Triarrhena lutarioriparia sample points were sampled to determine the biomass, carbon content and soil physical and chemical properties of 6 organs(panicles, leaf, stem, rhizome, root and bud), and analyze the relationship between plant carbon density and soil physical and chemical properties. The results showed that the biomass of stem was the highest and that of panicles was the lowest. The carbon content of above ground part is higher than that of underground part. The results also exhibited that the sequence carbon density of all organs of Triarrhena lutarioriparia from high to low was stem, root, rhizome, leaf, bud, panicles. Multiple linear regression analysis concluded that the carbon density of rhizomes had a positive regression relationship with soil pH, soil total K and organic matter content, and a negative regression relationship with soil moisture and electrical conductivity. The average carbon density of Triarrhena lutarioriparia had a positive regression relationship with soil total P content. Redundancy analysis(RDA) showed that the first ordination axis had a significant negative correlation with soil moisture and a significant positive correlation with pH. The second ordination axis was significantly positively correlated with soil total K content. In conclusion, the main carbon storage organ of Triarrhena lutarioriparia was stem and the main environmental factors affecting plant carbon density were soil moisture, pH, total phosphorus and total potassium contents. Therefore, soil conservation should be strengthened to maintain the carbon sink function of the wetland.