Abstract: The giant panda nature reserve play a momentous role in maintaining the biodiversity of its surrounding areas. A catastrophic earthquake happened in Wenchuan in the year of 2008 caused a severe ecological degradation in many panda's habitats nearby. Based on four phases of the Landsat images from 1998 to 2017 in Longxi-Hongkou National Nature Reserve, the study integrated principal component analysis method and four indicators including normalized vegetation index (NDVI), normalized difference built-up and soil index (NDSI), and land surface temperature (LST) to build a remote sensing ecological index (RSEI) and form a comprehensive evaluation model to synthetically assess the ecological environment status in the study area. The results show that the RSEI values of Longxi-Hongkou National Nature Reserve in 1998, 2007, 2008 and 2017 were 0.748 1, 0.752 1, 0.411 0 and 0.599 1, respectively. It indicates that the ecological environment in the study area got better first then deteriorated and improved at last during the period of 20 years, but the overall trend was in a degraded state. It is noteworthy that the ecological environment changed significantly before and after the earthquake, especially the ecological environment in the hilly and subalpine areas with an elevation of 1 400-2 600 m showed an obvious deterioration trend, mainly because the vegetation distruction caused by the earthquake, which has resulted in the reduction of water area and the formation of bare land. Green degree and wetness have positive effects on the key factors affecting the ecological environment, while dryness and heat have negative effects on the ecological environment.