The sustainable development of tourism has significant importance on the natural complex ecosystems and lives of humans and now become a global demand. The contradiction between eco-environmental protection and tourism development in vulnerable ecological regions is particularly salient. It is urgent to evaluate the development sustainability of tourism in such areas, which could promote the coordinated development of tourism economy and ecological protection. Taking Gannan Tibetan Autonomous Prefecture as the research area, this paper incorporates an emergy analysis and applies indexes such as Eti(tourism emergy income), Ete(tourism energy export), TELR(tourism environment load ratio), TEER(tourism emergy exchange ratio), and TSEI(tourism sustainable emergy index) to evaluate the development sustainability of tourism in Gannan from 2006 to 2015. This research results were concluded based on the survey data, the statistical data and the data from the emergy transformation. This research attempts to enhance the quantitative study on the sustainable development of tourism and provide a scientific underpinning for the comprehensive evaluation and sustainable management of vulnerable ecological regions. The findings are as follows:(1) from 2006-2015, the emergy value increased in tourism input and output per year in Gannan. Emergy for rigid demands, such as the demands for catering services and accommodations, accounted for 59%-82% of the total output emergy. This constitutive structure was unfavorable to sustainable development. (2) During this period the sustainability of the researched area was unstable. From 2006-2008, the TSEI declined from 2.49-0.94. A large consumption of nonrenewable resources caused great pressure on the environment, rendering the tourism development in this area unsustainable. From 2008-2015, the TSEI rose to7.85, and the tourism development in this area was changed to a sustainable pattern. However, from 2014-2015, the effective emergy output efficiency was still low, which indicated poor sustainability of tourism system in Gannan.