Abstract: Global natural environment changes and increasing human activities have greatly affected the ecological environment, leading to the emergence of many ecological problems and the high attention of the ecological vulnerability. The Qilian Mountains region is an important part of the plateau ecological security barrier in China, which guarantees the ecological security in the northwestern region of China. This region is characterized by the typical continental climate with low rainfall and dry climate, where the ecological environment has been seriously influenced with social and economic development and frequent human activities. In 2008, the government issued relevant plans for the ecological management and restoration of the Qilian Mountains region. Therefore, it is of great significance to evaluate and analyze the ecological vulnerability of the Qilian Mountains region in the three phases of 2005, 2010, and 2015. In this paper, according to the ecological environment characteristics of the Qilian Mountains, the operability and relevance of the evaluation indexes and the“sensitivity-resilience-stress”conceptual model of eight indicators of NDVI, topographic fluctuations, ground fragmentation, surface roughness, and topographic factors, as well as precipitation, temperature, meteorological factors, population density, and per capita GDP selected from natural and human aspects, using remote sensing and GIS technology, the principal component analysis method is used to obtain weights and ecological vulnerability Based on the ecological index and the ecological characteristics of the study area, and based on the existing ecological vulnerability assessment standards at home and abroad, the degree of ecological fragility in the Qilian Mountains during the past 10 a is systematically and quantitatively analyzed. The study's aim is to provide references for regional ecological protection, resource utilization, and sustainable development. Results showed that: (1) From the perspective of ecological vulnerability distribution in the study area, the degree of vulnerability is gradually weakened from northwest to southeast. The vegetation coverage in southwest is small and the high altitude and the poor ecological environment is the reason for the high degree of vulnerability. (2) For the ecological vulnerability of the whole region, the Qilian Mountains is mainly characterized by mild and severe vulnerability, and the degree of ecological vulnerability has gradually decreased in the past decade. (3) The ecological vulnerability of Qilian Mountains in 2005 is relatively high with the extremely fragile area of 28 610 km2, which dropped to 11 723 km2 in 2010 and 6 174 km2 in 2015. (4) The ecological vulnerability index of the study area was 3.307 in 2005, 3.118 in 2010 and 3.103 in 2015, showing a gradual decline trend. (5) The impacts of eight indicators on ecological vulnerability are all significant, and the difference is reflected in different periods. The vegetation index has the greatest impact on ecological vulnerability in 2005—2015, followed by precipitation, and the topographic factor has the least impact. In general, the ecological vulnerability of the Qilian Mountains has been reduced in recent years due to the introduction of relevant national plans. There has been some progress in the protection and comprehensive management of ecological environments. However, it is still necessary to strengthen the environmental protection, build the ecological security barrier, maintain the ecological security, and achieve a virtuous cycle of the ecosystem in the Qilian Mountains to promote the harmonious development of human and nature.

Key words: ecological vulnerability, SRP conceptual model, ecological remote sensing, principal component anal? ysis, Qilian Mountains