The "Grain to Green" project has been implemented for more than 20 years in the loess hilly region. However, its carbon sequestration effect is rarely evaluated. To this end, a total of 147 sample sites were collected in different topography (hillslope, gully shoulder, and gully) and vegetation types (secondary grassland, abandoned apricot forest, and abandoned slope cropland) in a small watershed in the region to collect samples from 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100 cm soil layers. The distribution characteristics of soil organic carbon (SOC) and the influence of topography and vegetation were studied by statistics and geostatistics. The results showed that the average SOC content in the 0-100 cm profile of Xifuzigou watershed was 2.43 g/kg. Topography and vegetation types had important effects on the distribution characteristics of the SOC in small watershed. The SOC content in the surface and profile of gully shoulder was the highest and significantly higher (P<0.05) than gully, but had no significant difference with hillslope. The SOC in the surface layer (0-20 cm) and subsurface layer (20-40 cm) of the secondary grassland was significantly higher (P<0.05) than that of abandoned apricot forest and abandoned slope cropland. Geostatistical analysis showed that the 0-20 cm soil layer had the largest nugget and the nugget coefficient was 49.6%, and the 0-100 cm profile's nugget coefficient was 15.7%. The results indicated that the surface SOC had the largest nugget effect and was influenced by both structural and random factors, and the profile SOC had strongly spatial correlation which distribution was dominated by structural factors. The distribution pattern of the SOC in 0-100 cm profile was similar to that in surface soil which high values of SOC content were distributed in the secondary grassland and abandoned apricot forest, while the low values were mainly in abandoned slope cropland and dam land. At the small watershed scale, the distribution of SOC was consistent with vegetation types, but had no significant correlation with microtopography (slope, aspect and position), which indicated that the land-use/land cover dramatic changes weakened the effect of topography on SOC distribution. However, the results cannot reflect the carbon sequestration effect in the region because there are great differences in landform in the loess hilly region, and the implementation of the project varies greatly in shape and form. In conclusion, the carbon sink effect of "Grain to Green" is significant, and presents significantly spatial heterogeneity under the effect of terrain and vegetation type.