Shrub encroachment significantly influences the structure and function of alpine meadow ecosystems in the Tibetan Plateau (TP); however, the combined effects of shrub expansion and climate on soil organic carbon (SOC) in these ecosystems remain largely unexplored. To address this gap, we investigated SOC content across elevation gradients (from 4311 to 4992 m a.s.l.) in both shrub-encroached and non-encroached plots at two sites, Yangbajing and Gongtang, which differ in precipitation levels. Both sites are located within the Plateau Subfrigid Arid and Semiarid Region (PSASR) of the TP. As a result, at both locations, shrub encroachment increased woody plant biomass, root biomass at 20-40 cm depth, species diversity, and soil nutrient levels, while reducing herbaceous biomass and surface root biomass (0-20 cm). These increases were strongly linked to surface soil carbon accumulation. Additionally, shrub encroachment substantially increased SOC content at both sites, with the disparity between encroached and non-encroached plots widening as precipitation increased, especially in Gongtang. Furthermore, increased soil moisture can shift the impact of shrub encroachments on plant and soil indicators from neutral to positive stances, again notably in Gongtang. This research underscores the regulatory role of moisture conditions in regulating soil carbon content within shrub-encroached alpine meadows on the TP.