Significance of the organic carbon pool in the soil in the study of global change is well recognized. Characteristics of the distribution of organic carbon in soil profile and methods of its assessment are the premise for precise calculation of the pool in the soil. On the basis of the results of the second national soil survey in China, a soil-organic-carbon-based database was established, and characteristics of the distribution of organic carbon in soil profile and methods for assessing organic carbon in soils of different soil taxonomic units were discussed, thus providing a scientific basis for rational and accurate calculation of the density of soil organic carbon and organic carbon pool in the soil.