A concept of grassland green carrying capacity was proposed with considerations to national park based on grassland carrying capacity. A conceptual framework of grassland green carrying capacity composed of ecological functional maintaining+forage-livestock balance+ecological experience to solve problems of how to solve population diversity and reproduction of wild animals, improve living standards of herdsman after the implementation of reduced-livestock and forbidden-grazing policy, and protect the increasing ecological experience or tourism economic development demands. Moreover, an evaluation index system of grassland green carrying capacity was constructed from five perspectives of supporting conditions of ecosystem, grassland productivity, carrying capacity scale of wild animals and livestock, and carrying capacity scale of peasants, herdsmen and ecological experience population, and monitoring and warning. A case study based on the Three-River-Source National Park was carried out. Research conclusions provide theoretical references to formulate scientific construction plans and development goals, and promote ecological protection and sustainable regional development of the Three-River-Source National Park.