Abstract: Aohan Banner is located in the farming-pastoral ecotone in Chifeng City, Inner Mongolia, soil types are rich, the area of artificial afforestation is large, and the carbon balance situation of planted forests in various soil types is quite different. In this experiments 3 sample plots were selected from the 6 soil types separately, and 5 sample sites were determined along the S-shaped sample line in each sample plot so as to study the distribution of soil organic carbon density in Aohan Banner. The conclusions are as follows: The organic carbon density of cinnamon soil was the highest, and that of Aeolian sandy soil was the lowest. The change trends of soil organic carbon density of cinnamon soil, chestnut soil and brown soil were different due to the difference in soil properties, slopes and slope positions. The organic carbon density of these soils was the highest on north slope but the lowest on south slope. The results of principal component analysis on the soil organic carbon density revealed that the slope was not as the main ingredient. Through regression analysis, it was concluded that the regression equations of the organic carbon density of three types of soil at significance level of P<0.05 are as:Y=25.662 40+1.722 06X₁-0.061 54X₂(R²=0.853 5) for cinnamon soil, Y=24.890 95-3.437 45X₁-0.002 12X₂(R²=0.899 5) for chestnut soil, and Y=19.112 05-0.090 72X₁-0.018 44X₂(R²=0.794 4) for brown soil.

Key words: soil types, terrain factor, organic carbon density, farming-pastoral ecotone, Inner Mongolia