Keystone species play a decisive role in community structure, function and stability. This research monitored and analyzed the changes of plant community characteristics, soil physicochemical property and soil enzyme activities under five grazing management regimes commonly used on the Qinghai-Tibet Plateau, which included grazing exclusion (GE), grazing during the dormant season (GD), traditional grazing (TG), grazing during growing period (GG) and continued grazing (CG). The network analysis and variance decomposition were used to explore the characteristics and driving factors of plant keystone species under different grazing regimes. The multi-criterion decision model TOPSIS was used to comprehensively evaluate different grazing regimes, so as to explore a grazing management that not only could effectively utilize grassland resources but also maintain high plant community diversity and stability on the Qinghai-Tibet Plateau. The results showed that: (1) compared with CG, the other four grazing regimes had significantly positive effects on the gramineae, leguminosae, litter, forbs, community above- and below-ground biomass, plant height, gramineae cover, diversity, soil nutrient content and soil enzyme activity. (2) The plant keystone species was Elymus nutans in GE site. The plant keystone species was Poa crymophila, Kobresia humilis and Leymus secalinus in GD site. It was Leymus secalinus, Kobresia humilis, and Stipa aliena in TG, GG, and CG site, respectively. Furthermore, the highest relationships between species in plant communities, interaction intensity, community organization level and stability were in GD site. (3) The variance decomposition showed that soil cellulase, urease and catalase were the most important factors affecting the changes of key species in the alpine meadow. (4) The multi-criterion decision model TOPSIS showed that GD could not only effectively utilize grassland resources, but also maintain high plant community diversity and stability, which was the best management strategy for the alpine meadow on the Qinghai-Tibet Plateau. The results provide scientific data support for the formulation of scientific grazing management system and the maintenance of grassland ecosystem stability and versatility.