Abstract: The ecological situation in Sanjiangyuan area has an important influence on China’s national economy and ecology. Besides, studies on the ecological environment vulnerability also have its own theoretical and practical significance. Based on ecological sensitivityresiliencepressure (SRP) conceptual model, we selected sixteen evaluation indices (including temperature, precipitation, topography, etc.) and established the indicators system of ecological vulnerability evaluation in Sanjiangyuan area using the AHP method and the principal component analysis (PCA) method. Through calculating the ecological environment vulnerability index (EEVI), we conducted vulnerability analysis and evaluation of ecological environment in the study area. The results showed that, in the study area, moderately vulnerable areas occupied 45.55% of the total, while the slightly, lightly, heavily and extremely vulnerable areas occupied 5.76%, 23.12%, 20.14% and 5.43% respectively. The heavily and extremely vulnerable areas are primarily located in the bare soil and low vegetation coverage zones of the northwest part of Sanjiangyuan area and in the northeast part under the greater pressure of large population and economic activities.

Key words: spatial and temporal change, ecosystem service value, terrain gradient effect, middle reach of Yangtze River.