Density of soil organic C pool and its variation in the soils under different types of landuse were investigated through field sampling and chemical analysis at the Ecological Experimental Station of Red Soil, Chinese Academy of Sciences. Results showed that in hilly red soil organic C density was (2.09 ±0.69) kg/m² and (5.01 ±1.46) kg/m², and total N density (0.20 ±0.07) kg/m² and (0.59 ±0.14) kg/m², in the soil layer of 0~20cm and 0~100cm in depth, respectively, which varied with the landuse. Soil organic C density in the soil layer of 0~20cm and 0~100cm in depth increased by 1.0kg/m² and 1.7kg/m² in sparse grassland compared to that in bare land, by 0.7kg/m² and 0.9kg/m² in artificial forest or orchard compared to that in sparse grassland, and by 2.3kg/m² and 4.4kg/m² in paddy field of high fertility compared to that in sparse grassland. Differences also existed in organic C density being 1.0kg/m² and 3.5kg/m² between different types of artificial forests and orchards. The difference between profiles in organic C density being 1.3kg/m² and 2.9kg/m² and in total N density being 0.1kg/m² and 0.3kg/m², and between soils different in fertility in organic C density being 1.5~2.2kg/m² and 2.8~4.1kg/m² and in total N density being 0.07~0.11kg/m² and 0.20~0.23kg/m². Intensive erosion could decrease soil organic C density by 1.4kg/m² in the soil layer of 0~20cm and by 2.2kg/m² in the soil layer of 0~100cm in depth. Therefore, rationalization of land use could increase the density of soil organic C pool and enhance the potential of sequestrating atmospheric CO₂ in soil.