We determined active organic carbon (microbial biomass carbon, MBC; easily oxidized carbon, EOC; and particle organic carbon, POC) and organic carbon in four typical vegetations (grassland, Xanthoceras sorbifolia, Caragana korshinskii shrub, and Hippophae rhamnoides) in the hilly-gully region of the Loess Plateau. The results showed that the soil organic carbon content during planting gradually decreased as the soil depth increased, Xanthoceras sorbifolia > grassland > Caragana korshinskii shrub > Hippophae rhamnoides, and the difference was significant (P < 0.05). The soil MBC content in the 0-40 cm soil layer of the grassland was significantly lower than that in Xanthoceras sorbifolia, Caragana korshinskii shrub, and Hippophae rhamnoides by 8.61%, 23.84%, and 41.42%, respectively (P < 0.05). The POC content in the grassland soil was 14.47% and 16.67% lower than that in Xanthoceras sorbifolia and Hippophae rhamnoides, respectively, and 25% higher than that in Caragana korshinskii shrub; however, the EOC content, carbon activity, and carbon management index were significantly higher in the grassland than in the other three vegetation types (P < 0.05). The soil microbial entropy(SME) of Hippophae rhamnoides in the four vegetation types was the highest, and soil organic carbon of Caragana korshinskii shrub was the lowest. Soil SOC was extremely significantly correlated with soil EOC,soil organic carbon storage (SOCS) (P < 0.05), whereas soil SOC was significantly correlated with POC (P < 0.01) and soil EOC with soil POC (P < 0.05). However, soil MBC and SOC, POC, EOC, and SOCS showed different degrees of negative correlation. Therefore, soil active organic carbon can objectively reflect the changes in soil fertility and quality, and it is an important index to describe soil quality and evaluate soil management.