According to the data from the second soil survey of Yunnan Province, the soil organic carbon(SOC) density and storage were estimated with soil type method; Meanwhile the spatial distribution of SOC density in Yunnan Province and the main factors on SOC density were analyzed. The results showed that the SOC density estimated in the 0-20 cm layer was 59.77 t/hm² and stock was about 2.30×10⁹ t; and the SOC density estimated in the 0-100 cm layer was 159.95 t/hm², its storage was about 6.15×10⁹ t accounting for 7.28% of the total in China and 0.41% of the global terrestrial ecosystems; the top four soil types in SOC storage were red soil, yellow-brown soil, lateritic red soil and brown soil totally taking up about 60% of that in Yunnan Province. The spatial distribution pattern of SOC density was the highest in Yunnan Province was in the northwest and northeast of Yunnan Province, followed by east of Hengduan Mountains and the western Yunnan plateau, and that of the purple soils in the north central area was the lowest. Otherwise, due to the impact of rainfall, temperature, elevation and land use types, the distribution of SOC density in the region was uneven. Furthermore the natural factors such as rainfall, temperature and elevation were the main factors affecting SOC density.