China has the largest plantation area in the world. Under the background of global warming, there are more and more concerns on carbon storage ability of plantations. In this paper, Huitong National Research Station of Forest Ecosystem with long-term observational data was chosen as the study area. The carbon density and allocation of each composition (tree, understory vegetation, litter, soil) of nine forest ecosystems including eight plantations with age ranging from 25 to 32 years (Cunninghamia lanceolata, Pinus massoniana, Pinus elliottii, Cunninghamia lanceolata and Cinnamomum camphora, Cunninghamia lanceolata and Michelia macclurei, Pinus massoniana and Schima superba, Schima superba, Michelia macclurei) and one natural forest with average age of 63 years (Castanopsis fargesii, Cyclobalanopsis glauca and Machilus pauhoi) were analyzed and compared. The results showed that: 1) the average density of ecosystem carbon at Moshao forest farm was 261.61 t/ hm~2, which indicated that forest ecosystem of Moshao forest farm had a relative high ability of carbon storage. The Pinus massoniana and Schima superba mixed forest and Cunninghamia lanceolata and Michelia macclurei mixed forest had the highest ecosystem carbon density, and the natural forest ranked the fifth. 2) The majority of carbon density of Moshao forest farm was stored in the tree layer and soil layer, accounting for 98.23% of the total carbon density of the forest ecosystems. The understory vegetation and litter had little contribution to ecosystem carbon density. 3) Carbon storage of trunk in the tree layer was the highest, followed by root and brank, and then bark. The proportion of carbon density and allocation declined as the soil depth increases, and carbon was mainly stored in the layer of 0-20 cm.