Abstract: Based on the data of the multi-purpose regional geochemical survey in the Songliao Plain, Northeast China,the authors calculated the soil organic carbon density and reservesin surface soil(0~20 cm) and compared them with the soil organic carbon density obtained during the second national soil survey. Then it analyzed the main influencing factors of the distribution and changes of the soil organic carbon density in the plain. The results are as follows. The surface soil of different soil types in the Songliao Plain significantly differ in the proportion of organic and inorganic carbon. Specifically, the organic carbon in swamp soil, dark brown soil, peat soil, albic soil, paddy soil, and black soil accounts for 90% of the total carbon in soils, while that in chestnut soil, fluvo-aquic soil, aeolian sandy soil, and cinnamon soil accounts for less than 80% of the total carbon content. The organic carbon reserves in the surface soil in the study area is about 1,448 Tg at present. It has suffered a loss of about 115.94 Tg since the 1980s, decreasing by 7.4%. About 104.88 Tg (90.5%) of the lost carbon reserves has entered into the atmosphere. In terms of different land use types,the carbon reserves in arid land decreased by 76.12 Tg, which contributed the most CO₂ to the atmosphere, followed by the carbon reservesin saline land and grassland, which decreased by 16.32 Tg and 15.93 Tg, respectively. It is considered in this study that the main reason for the decrease in soil carbon pool is the temperature rise in the Songliao Plain in the past 30 years. In detail, the reduction in soil organic carbon pool in arid land and grassland induced by the temperature rise accounted for 70% of the total loss of soil organic carbon pool, while the reduction in organic carbon caused by other factors such as agricultural production, change in land use, and soil erosion accounted for only about 30% of the total organic carbon loss.