Changes in major fractions of active soil organic carbon (ASOC) and effects of soil microbes on ASOC in the surface layer (0~10 cm) and the subsurface layer (10~20 cm) of alpine steppes different in state (normal, lightly and severely degenerated) in the north Tibetan Plateau. Results show that significant differences were found between readily oxidation carbon (ROC), microbial biomass carbon (MBC), light fraction of organic carbon (LFOC) and water soluble organic carbon (WSOC) in response to changes in soil environment. Their respective mean distribution ratio was11.10%, 0.57%, 0.04% and 0.03%. The cold dry environment of the plateau was not favorable to formation and accumulation of WSOC and LFOC. Regardless of state of the steppes, contents of the various fractions of organic carbon were higher in the surface layer than in the subsurface layer. Compared with the contents of the various fractions of organic carbon in normal steppes, those in degraded steppes were slightly higher in the surface layer, but significantly lower in the subsurface layer, and the changes were greater in mildly degraded steppes, showing a decreasing order of normal steppes > severely degraded steppes > lightly degraded steppes in terms of content of organic carbon in the 0~20 cm soil layer. In steppes of all states, cellulolytic enzymes played a significant promotive role in formation of the fractions of ASOC ( R²: 0.731~0.960), whereas activity of the cellulolytic enzymes was much affected by soil actinomycetes and fungi. In seriously degraded steppes, soil microbes may have completed their succession into microbial populations that were much higher in stress resistance and cellulolytic enzyme secretion ability. And the relatively higher SOC and ASOC contents in the steppes characterized greater consumption of organic residues in the soil.