Garzê Tibetan Autonomous Prefecture (hereafter Garzê) is located along the upper reaches of the Yangtze River, a unique geographical location that contributes to the prefecture's complex and diverse landscapes and rich biodiversity. Garzê possesses hydropower resources, which comprises thousands of rivers and can be divided into three parts: Jinsha River, Yalong River, and Dadu River. Owing to its important ecological location, Garzê has many ecosystem functions, such as water retention, soil retention, flood mitigation, the protection of biological diversity. Although the ecological condition of Garzê is excellent, the prefecture's economy has lagged behind that of the rest of the country, and many of the important ecosystem products and services that it provides have not been fully recognized or adequately quantified. Therefore, assessing Garzê's ecosystem services is both essential and urgent and will contribute to the sustainable development of the prefecture's society and economy. In this study, Garzê's ecosystem services were divided into three categories (ecosystem provisioning, regulating, and cultural services), and Garzê's gross ecosystem product (GEP) was evaluated using the market value, replacement cost, and travel cost methods, among others, in order to assess the direct contribution of Garzê's ecosystem to beneficiaries. Our results indicated that the GEP of Garzê was 754.559 billion Yuan in 2010 and that the per capita GEP was 711,800 Yuan, which is about 61 times the prefecture's gross domestic product (GDP) and per capita GDP of the same year. Among the ecosystem services, the total value of ecosystem-regulating services was the largest, at 684.228 billion Yuan and accounting for 90.68% of the prefecture's GEP. The total value of ecosystem provisioning services and cultural services was 63.264 billion Yuan and 7.067 billion Yuan, respectively, accounting for 8.38 and 0.94% of the prefecture's GEP. In terms of types of services, water retention, climate regulation, and carbon sequestration-oxygen release were the core services, with a total value of 84.38% of the prefecture's GEP, thus confirming Garzê's high plant cover and function as a significant water retention area of the upper reaches of the Yangtze River. In terms of types of ecosystems, the values of the ecosystems were ranked as follows: Grassland > Forest > Shrub > Wetland > Farmland > Bare land > Glaciers and snowfield > Town; and the total value of the Grassland, Forest, Shrub, and Wetland was 98.87% of the prefecture's GEP. This indicated that these four ecosystems are the main source of ecological products and services; contribute vast economic value to human society and, therefore, to the process of resource development and management; and deserve relatively more attention than other ecosystem types. Our study suggests that Garzê's ecosystem services are highly valuable and that protecting the prefecture's ecosystem will also protect human welfare. The findings of the study can be applied to administrative policymaking and environmental protection, and it will provide a scientific basis for the management, protection, and compensation of the region's ecosystems.