Abstract: The Salix triandroides and Carex brevicuspis communities in Dongting Lake wetland with three gradient of ground water level were studied, the comparison revealed the content of soil organic carbon and the composition of humus carbon (Humic acid carbon, Fulvic acid carbon and Humin carbon) in the four soil layers (0-20, >20-40, >40-60 and >60-80 cm) of the two plant communities. The results show that:(1) The content of organic carbon and humus carbon in the soil of two species of plant communities was higher at 0-20 cm soil layer. (2) In general, the organic carbon content of the four soil layers in the Carex brevicuspis community was higher in the middle water level area, while in the Salix triandroides community the 0-20 cm soil layer was higher in the high water level area, and the >20-80 cm soil layer was higher in the middle water level. There was no significant difference in the content of fulvic acid carbon between the three water levels in the Salix triandroides community and Carex brevicuspis community. The Salix triandroides community 0-20 cm soil humic acid and humin carbon content in high water level was higher, >60-80 cm soil humic acid carbon content in high water level was low, and >20-40 and >40-60 cm soil layer under the water level of three kinds of humic acid carbon content had no significant difference, in the three-layer of >20-80 cm were all low in high water level. Carex brevicuspis community soil humin carbon content is higher in middle water level area, 0-20 and >20-40 cm soil layer of the carbon content of humic acid in middle water level is higher, >60-80 cm soil layer with high water level is low, 40-60 cm soil layer humin carbon content under the three kinds of water level had no significant difference. (3) In each component of humus, humin carbon content was the highest in both plant communities. (4) Compared with Carex brevicuspis community, Salix triandroides community can improve the low water level area 0-80 cm, and high water area 0-20 cm of soil organic carbon and humus carbon content, but reduces the middle water level in the 0-80 cm, and high water level >20-60 cm soil organic carbon and humus carbon content. So that, the soil carbon of wetland is affected by the comprehensive vegetation type and water level gradient, and it is needed to combine with the hydrological characteristics to scientifically evaluate the soil carbon of wetland.