Grassland ecosystem carrying capacity (GCC) is directly related to herdsmen's livelihood, and the implementation of ecosystem conservation and restoration programs. It is particularly concerned widely in the Qinghai-Tibet Plateau (QTP) due to its unique location conditions and important ecosystem services. To investigate the spatiotemporal patterns and early-warning of GCC in the QTP, we calculated the theoretical livestock carrying capacity, and defined the early-warning level of GCC based on the net primary productivity (NPP) in the QTP and livestock inventory in 236 counties from 2000 to 2015. The results showed as follows:(1) the GCC in the east was higher than that in the west in the QTP. The theoretical livestock carrying capacity of alpine grassland and alpine meadow accounted for 64.99% of the total, and they were the main components of theoretical livestock carrying capacity. (2) The theoretical livestock carrying capacity increased from 86.15 million sheep units (SU) to 91.18 million SU from 2000 to 2010, and then increased to 94.52 million SU from 2010 to 2015. The theoretical livestock carrying capacity increased by 9.71% in the past 15 years. And the theoretical livestock carrying capacity in the northeast increased the most, but the theoretical livestock carrying capacity in the west was basically stable in the QTP. (3) The GCC had always been overgrazed in the QTP. The livestock inventory increased from 144.90 million SU to 163.85 million SU from 2000 to 2010, and then decreased to 158.46 million SU from 2010 to 2015. The livestock inventory increased by 9.36% in the past 15 years. The Balance of Grassland and Livestock Index (BGLI) increased from 67.88% to 79.90% before 2010, and then slightly eased in 2015 (67.91%). The spatial pattern of GCC was consistent with the early-warning pattern. The numbers of green no early-warning zone, blue early-warning zone, yellow early-warning zone, orange early-warning zone and red early-warning zone were 32, 9, 4, 119 and 72, respectively. The green no early-warning zone was located in the west and north, meanwhile, they were always the pastoral and semipastoral areas in the QTP. At present, we should give priority to control the livestock in the red early-warning area since they were overgrazed and their BGLI were still increasing. In the future, it is necessary to improve the GCC and maintain the sustainable development of grassland ecosystem by controlling the livestock inventory, adjusting the development pattern of animal husbandry and enhancing grassland productivity in the QTP.