【Objective】Soil aggregate is an important storage unit of soil organic carbon, and its stability directly affects the sequestration of organic carbon. This study explored the effects of shrub encroachment on the stability of soil aggregates and their cementing materials in grassland.【Method】The content of soil aggregates and their cementing materials (soil aggregate organic carbon, Fe-Al oxides, Ca bond organic carbon, and Fe-Al bond organic carbon) and the stability of aggregates (the content of aggregates >0.25 mm, mean weight diameter/MWD and fractal dimension)were determined at four typical shrub-encroached grasslands(Spiraea alpina, Sibiraea angustata, Caragana microphylla, Potentilla fruticosa) in the eastern margin of the Qinghai-Tibet Plateau. 【Result】 The results show that shrub encroachment significantly decreased the aggregate content of 2～0.25 mm and <0.002 mm and aggregate stability in the Caragana microphylla plot. However, there was no significant effect on the other three shrub grasslands. Shrub encroachment mainly changed the content of cementing substances in the aggregates of the Caragana microphylla and Sibiraea angustata plot. The results of boosted regression tree analysis between cementing materials and MWD show that the main contributing factors to the stability of aggregates in Spiraea alpina polt were complexed iron (Fe_p) and amorphous iron and aluminum (Fe_o, Al_o). Also, the major contributors to grassland and other shrub plots were soil aggregate organic carbon (SAOC) and free iron oxides(Fe_d). 【Conclusion】 Although shrub encroachment increases the content of main cementing material—SAOC in <0.053 mm in Caragana microphylla plot, it reduced the content of large aggregates and clay, as well as the content of Fe_d in the Caragana microphylla plot. Thus, the stability of aggregates is reduced, which may be detrimental to the retention of organic carbon. This study provides theoretical knowledge for the stability theory of aggregates and the dynamic change of the organic carbon pool in this region.