The disorderly development of natural resources and the destruction of ecosystems inhibit China's sustainable development. Resource carrying capacity is an important tool to describe the development of regional resources and is also a fundamental basis for measuring regional sustainable development. Based on the statistics of the counties in the Three-Rivers Region in Tibet, this paper quantitatively calculates the resource carrying capacity of water, soil and ecology, and builds a monitoring system for resource carrying capacity based on quantitative evaluation results and applies it to the Three-Rivers Region in Tibet. The results show that: (1) The relationship between population and food in the study region tended to be tense. The population-food-land contradiction was prominent in some counties. Land resource carrying capacity in 76.5% of the counties declined, and land resource carrying indexes for 83.3% of the counties increased. The water resource carrying capacity in the study region was much larger compared with the actual population, and the water resource carrying indexes were less than 0.05, but the water resource carrying capacity in 77.8% of the counties decreased, and the carrying indexes increased. The ecological carrying capacity of each county increased, the carrying indexes decreased, and some counties were in an ecological deficit state. (2) The main constraints of resource carrying capacity in the study region were transformed from ecological carrying capacity to land resource carrying capacity. From 2000 to 2015, among the counties where the resource carrying capacity was critically overloaded or overloaded, the resource carrying capacity that had the greatest impact on the resource carrying status was gradually transformed from the ecological carrying capacity to the land resources carrying capacity. (3) The level of resource carrying capacity in the region gradually increased, and the degree of harm or negative impact may be reduced. From 2000 to 2015, the number of counties with a resource carrying capacity of three (medium load) and below fell from 15 (83.3%) to 3 (16.7%). The establishment of a long-term monitoring mechanism for resource carrying capacity helps to clarify the status quo of resource development and utilization, scientifically utilize regional natural resources, and promote regional ecological protection and sustainable development.