Abstract: We analyzed the relationship between ecological quality change and climate and topography in Helan Mountain from 1989 to 2017, with multitemporal Landsat data, RSEI (remote sensing ecological index), SRTM DEM data, Chinese meteorological data and spatial distribution data of vegetation types. The RSEI obtained by coupling WET, NDVI, SI and LST could comprehensively reflect ecological quality, with the load value of NDVI being the highest. From 1989 to 2017, the average value of RSEI in the study area showed an uptrend, with a range of 0.2849-0.3671 and an annual growth rate of 0.0058. The RSEI-improved area was 14.6 times of the RSEI-degraded area. The excellent and good levels of RSEI were mainly distributed in forest areas, while the variation coefficient of eco-environment in these regions was small. The moderate, low and poor grades of RSEI were mainly distributed in desert and grassland covered areas, which were mainly the areas of ecoenvironment improvement. A total of 9.29% areas with correlation between RSEI and temperature passed the significance test (P<0.05), and 12.51% of the areas with correlation between RSEI and precipitation passed the significance test (P<0.05). Theresponse of RSEI to precipitation was stronger than that to temperature. The best ecological quality area of Helan Mountain was located in altitude 2500-3000 m and slope 35°-40°. Although the ecological environment of Helan Mountain is slowly getting better, the overall ecological quality is still extremely fragile. There is still a long way to go for ecological protection in this area.

Key words: Helan Mountain, ecological quality, remote sensing ecological index, climate change, terrain effect.