Grazing could alter plant primary production and carbon (C) storage in Alpine meadow ecosystems. The grazing optimization hypothesis (GOH) suggests that aboveground net primary production increases at a moderate grazing intensity. In this study, GOH was tested by investigating the responses of plant production and ecosystem C storage to grazing intensity. The results indicated that both the root biomass and total biomass reached the highest values in moderate grazing (MG), and the species richness, root to shoot ratio (R:S ratio) increased in MG, suggesting that more assimilates allocated from aboveground to belowground under MG. Similar plant material carbon concentrations were observed for all of the grazing intensities (i.e., 40-50%), and the soil organic carbon (SOC) storage depended on the root biomass. The soil organic C storage and ecosystem C storage both peaked with MG, which supported GOH. Thus, moderate grazing promoted ecosystem C sequestration by altering the plant community structure, plant production and R:S ratio in the Alpine grassland.