【Objective】Changes in the dominant vegetation community will inevitably affect soil organic carbon (SOC) by altering the quantity of litter and root exudates during shrub encroachment. Thus, this study aimed to explore the response of different active organic carbon fractions in alpine grassland soils to invasion by different shrub species.【Method】Physicochemical fractionation method was used to divide soil organic carbon into non-protected carbon, physically-protected carbon, chemically-protected carbon and biochemically-protected carbon. It was analysed the contents of various organic carbon fractions and factors influencing their contents among four typical shrub-grassland and unshrub-encroached grassland on the east edge of Qinghai-Tibetan Plateau.【Result】The results showed that (1) Shrub encroachment has no significant effect on the SOC content of the surface soil(0-10 cm)in alpine grassland (P>0.05), but the content of organic carbon components was different. After Spiraea alpina and Sibiraea angustata shrubs encroached the grassland, the non-protected organic carbon and biochemically-protected organic carbon contents were significantly decreased (P<0.05) while the non-protected organic carbon content significantly decreased when Potentilla fruticose encroached the grassland. Also, the contents of physically-protected and chemically-protected organic carbon decreased significantly in Caragana microphylla encroached grassland (P<0.05), while the biochemically-protected organic carbon increased significantly (P<0.05). (2) SOC in both grassland and shrub patches soil were dominated by non-protected carbon pool, followed by resistant carbon pool (chemically-protected organic carbon and biochemically-protected organic carbon), while physically-protected organic carbon pool accounted for the least. (3) The contents of soil clay and total nitrogen were the main factors affecting the organic carbon fractions in alpine shrub-encroached grassland, with an explanation degree of 51.2%. 【Conclusion】The invasion of different shrub species had inconsistent effects on the content of different reactive organic carbon fractions. The soils of both unshrub grassland and shrub sample sites on the Tibetan Plateau were dominated by non-protected carbon. Thus, in the presence of external disturbances, the organic carbon pool in the area may become a source of carbon.