In order to assess the influence of land use on soil carbon pool, natural grassland, artificial woodland (directly converted from natural grassland) and cropland (reclaimed from natural grassland) in Chernozem region of Northeast China, were taken as research objects. A total of 45 soil samples were collected from these three land use types. Five soil pedogenic horizons (A, AB, B_K, BC and C) in 0—100 cm soil were collected. Soil organic carbon (SOC), water soluble organic carbon (WSOC), light fraction organic carbon (LFOC), and heavy fraction organic carbon (HFOC) contents were determined. The results showed that the contents of SOC, LFOC, and HFOC were mainly distributed in horizon A, but the content of WSOC was the highest in horizon B_K, which was 0.27 g/kg. From horizon A to horizon C, SOC and its components contents of the three land use types all showed a decreasing trend, but the decreasing degree was obviously different. The grassland decreased slowly, the woodland decreased sharply, and the cropland decreased gradually. The contents of WSOC, LFOC, HFOC, and SOC decreased by 34% and 48%, 20% and37%, 7% and 5%, 10% and 16%, respectively, after the grassland were converted into woodland and cropland. After grassland was converted to woodland and cropland, WSOC/SOC and LFOC/SOC decreased significantly but HFOC/SOC increased, indicating that the content of active organic carbon decreased rapidly. Land use types and soil horizons had significant effects on SOC, WSOC and LFOC, and had strong superposition effects on SOC and HFOC. At the same time, soil physical and chemical properties also affected SOC, WSOC, LFOC and HFOC to some extent. Rational land use management policies should be formulated to protect natural grassland from destruction, and play an important role in carbon sequestration of grassland ecosystem.