Abstract: Taking Fugong County of Nujiang Lisu Autonomous Prefecture as the study area and using the 10 remote sensing images from 2000 to 2020 as data sources, the principal component analysis method is used to objectively weight the 4 indexes of greenness, humidity, heat, and dryness to generate RSEI, and the small watershed unit was taken as the evaluation unit to evaluate the eco-environmental quality of Fogong County from 2000 to 2020. The results show that the average RSEI of Fogong County shows a tortuous upward trend from 2000 to 2020. The proportion of ecological quality above the medium was generally on the rise; from 2000 to 2020, the proportion of ecological degradation, invariance, and improvement is 1.17%, 56.57%, and 42.26% respectively, the eco-environmental quality has improved based on overall stability, and the areas where the eco-environmental quality has improved are mainly concentrated on the east and west sides of the study area; in the study area, meteorological factors affect the ecological environment by affecting plant growth. Elevation and slope direction are the main natural factors that affect the quality of ecological environment, while woodland and cultivated land, as well as construction land, are the main land use ways that affect the quality of ecological environment.