The focus has been on afforestation and re-afforestation as new methods for improving carbon sequestration, by optimizing the mode of afforestation and adjusting the forest tree species composition. Carbon content and storage of different components, including tree, shrub, herb, litter, and soil layers and their allocations of a 26-year-old Castanopsis hystrix (PCH), Cunninghamia lanceolata (PCL), and mixed C. hystrix × C. lanceolata (MCC) stands in subtropical China were studied using quadrat sampling combined with biomass measurements. The results showed that the average carbon content of different organs in C. lanceolata and C. hystrix were 492.1-545.7 g/kg and 486.7-524.1 g/kg, respectively. Significant differences were found among different organs in the same tree species(P<0.05). The average carbon content of C. hystrix(539.3 g/kg)was higher than C. lanceolata. Carbon content of the ground cover was PCH>MCC>PCL. Soil content in 0-100 cm showed significant differences among the three stands, which was ranked as PCL > MCC > PCH(P < 0.05). The carbon storage in the total ecosystem was ranked as PCL(169.49 t/hm²)> MCC(141.18 t/hm²)> PCH(129.20 t/hm². Significant differences were found among different components in the same stand, and among different stands of the same components (P<0.05). Afforestation significantly affected the carbon storage and allocation in plantations, and the mixed stand benefited from increased carbon biomass and soil carbon for C. hystrix; while monoculture stand benefited from the biomass and soil carbon for C. lanceolata Therefore, we should select the afforestation mode based on the carbon acumination characteristics of tree species regarding carbon sequestration forests, because mixed stands do not always fix more carbon compared with pure forests.