[Objective] The succession of vegetation communities in the process of grassland encroachment by shrubs affects the soil organic carbon (SOC) pool, and these changes are quickly reflected by the active components of SOC. The effect of shrub encroachment on the active components of SOC in an alpine meadow was analysed to provide data support for the study of changes in the SOC pool and carbon sequestration in grasslands of the Qinghai-Xizang Plateau against the backdrop of global climate change. [Methods] Taking the Caragana erinacea shrub meadow in the Qinghai-Xizang Plateau as the research target, changes in the soil physical and chemical properties, carbon cycle enzyme activities, and SOC active components in the 0—10, 10—20 cm, and 20—40 cm soil layers at different shrub encroachment stages (non-shrub, moderate-shrub, and heavy-shrub meadow) were analysed. [Results] ① The soil water content (SWC) in the 0—20 cm layer decreased significantly by shrublading. Moreover, the SOC content in all soil layers was the highest in the heavy-shrub meadow. Additionally, the soil pH value increased significantly in the moderate-shrub meadow. ② The soil amylase activity (SAA) in the moderate-shrub meadow was significantly lower than that in the non-shrub meadow, and the soil sucrase activity (SSA) in the 10—40 cm soil layer was also significantly lower. SSA in the heavy-shrub meadow was significantly higher than that in the non-shrub meadow. ③ The readily oxidizable organic carbon (ROOC) contents in the 0—10, 10—20 cm, and 20—40 cm layers in the moderate-shrub meadow were 16.79%, 21.73%, and 31.11% lower than those in the non-shrub meadow, respectively. The dissolved organic carbon (DOC) and microbial biomass carbon (MBC) contents in the 0—10 cm layer also decreased significantly. The particulate organic carbon (POC) and ROOC contents in the 0—10 cm layer were 24.37% and 29.54% higher than those in the non-shrub meadow, respectively. The MBC and DOC contents in the 10—20 cm layer were 12.96% and 10.38% higher than those in the non-shrub meadow, respectively. The MBC and DOC contents in the 20—40 cm layer were 57.62% and 22.10% higher than those in the non-shrub meadow, respectively. ④ SOC active components were significantly positively correlated with TN, SWC, SOC, and carbon cycle enzyme activity, and ROOC was strongly negatively correlated with pH value. [Conclusion] The content of SOC active components decreased during the early stage of C. erinacea shrub encroachment in the study area, whereas SOC and its active components underwent accumulation during the later stage of shrub encroachment. This may have a positive effect on the accumulation of SOC and the improvement of soil quality in this area.