Abstract: Wetland ecosystem is one of three important ecosystem-types on the earth. To understand well the organic carbon accumulation mechanism and its cycling characteristics is the very basis and one of the most crucial research contents of global carbon cycling and global climate change. Some researches show that wetland ecosystem protection and restoration are helpful to carbon accumulation and greenhouse gases reduction, which to some extent can mitigate the negative effects of climate change. The paper put its emphasis on several closely interrelated issues, including wetland carbon stock, carbon balance and the effects of greenhouse gases emission, the relations between wetland ecosystem and global climate change, as well as an outlook of carbon cycle of the Dongting Lake wetland ecosystem.