Based on repeated sampling in a number of areas, variations of organic carbon (SOC), humus carbon (HC), humic acid carbon (HAC) and fulvic acid carbon (FAC) in the surface (0~10 cm) and sub-surface (10~20 cm) layers of alpine steppes different in state (normal, slightly degraded and severely degraded) in the Northern Tibetan Plateau as well as influences and effects of soil microbial community, microbial biomass carbon (MBC) and cellulolytic enzyme activity (CEA) on SOC, HC and HAC. Results show that the soil in cold and acid alpine environment is very low in HC/SOC ratio, but very high in PQ value (HAC/HC). On the whole, the contents of SOC, HC and HAC and the proportion of HC/SOC in steppes different in state declines to a varying extent with soil depth in profile, while PQ value increases to a certain extent. Relative to normal steppes, the increase in SOC declines slightly and in HC (HAC, FAC) rises dramatically in the surface soil layer, and both drop drastically in the sub-surface soil layer. In terms of contents of SOC, HC and HAC in the 0~20 cm soil layer, a decreasing ordeer of normal steppe ＞ severely degraded steppe ＞ slightly degraded steppe is found, and in terms of HC/SOC ratio and PQ value, a decreasing ordeer of severely degraded steppe ＞ normal steppe ＞ slightly degraded steppe, and of normal steppe ＞ severely degraded steppe ＞ slightly degraded steppe is respectively, which means degradation of a steppe promotes formation and accumulation of SOC and HC (HAC and FAC) in the surface soil layer, and also “stimulates” mineralization of the sub-surface soil layer, and especially decomposition of organic debris in severely degraded steppes. However, quality of the humus is not improved correspondingly along with the increasing degree of soil humification. The highly homogenous distribution MBC, CEA, SOC, HC and their components in the soil affects and decides the above-mentioned process. Steppe degradation is conductive to decomposition and transformation of organic debris in the soil by fungus and actinomycetes, especially in the sub-surface soil layer.