Secondary forests are one of the most important fast-growth forest types, with a large distribution area and high potential carbon sequestration capacity. In order to investigate the component characteristics of soil organic carbon in a subtropical secondary evergreen broad-leaved forest, an experiment was conducted in a typical evergreen broad-leaved secondary forest (Castanopsis platyacantha-Schima sinensis) in the middle section of Wawushan Mountain, southwest China. The physical soil properties and soil carbon fractions were studied, with the soil profile divided (0-10, 10-40, 40-70 cm and 70-100 cm) and sampled. Results showed that the soil at each level was acidic. Soil potential acidity was between 3.2 and 4.0, field moisture capacity was 63%-190%, and total porosity and bulk density were 63.0%-83.3% and 0.41-0.99 g/cm³ respectively. Soil pH value and bulk density increased with increased soil depth, while the field moisture capacity and total porosity showed the opposite trend. The organic carbon content of litter was 443 g/kg, and the litter stock and litter carbon stock were 10.4 t/hm² and 4.5 t/hm², respectively. Litter organic C stock in the studied forest was higher than in the majority of the plantations and natural forests in Sichuan Province. Soil organic carbon, microbial biomass carbon, extractable dissolved organic carbon, and readily oxidizable carbon decreased with an increase in soil depth. The soil organic carbon content in the 0-10 cm layer was 121.9 g/kg, which was higher than reported in other subtropical evergreen broad-leaved forests and in all types of forests in Sichuan (3.6, 8.6, and 14.6 times the soil organic content of the soil layers at 10-40 cm, 40-70 cm, and 70-100 cm respectively). The content of microbial biomass carbon in the 0-10 cm layer was 1931.82 mg/kg, which was 2.6, 5.7, and 7.8 times that in the following three layers. The contents of extractable dissolved organic carbon and readily oxidizable carbon in the 0-10 cm layer were 697.42 mg/kg and 20.98 g/kg, respectively. The contents of labile organic carbon in the 0-10 cm layer were higher than in many other reported similar natural forests and plantations. The density of soil organic carbon, microbial biomass carbon, extractable dissolved organic carbon, and readily oxidizable carbon were 7.5-48, 0.20-0.81, 0.25-0.37, and 0.8-8.4 kg/m³, respectively. The density of soil organic carbon, extractable dissolved carbon, and readily oxidizable carbon decreased with an increase in soil depth, while the microbial biomass carbon first increased and then decreased and peaked at the horizon, 10-40 cm. Soil organic carbon stock was 154.9 t/hm², which was at the mid-level in Sichuan Province. The stocks of microbial biomass carbon, extractable dissolved organic carbon, and readily oxidizable carbon were 3.1, 3.0 and 21.0 t/hm², respectively. This study suggests that (1) the content of the soil labile organic carbon was relatively high, (2) the activity of microorganisms and the flow of nutrients were relatively active, and (3) there is a huge amount of forest litter in the C. platyacantha-S. sinensis evergreen broad-leaved secondary forest that can be transformed into soil carbon in the future. These ecosystems will play a more important role in regional carbon cycles in the future.