Abstract: As the best instruction factor of vegetation coverage, NDVI is regarded as the most effective indicator to monitor regional or global change of vegetation and ecological environment. Based on MODIS NDVI data with spatial resolution of 250 m and climate data during the period from 2000 to 2011, in this paper the spatiotemporal change of vegetation coverage and its correlations with climatic factors in the Qilian Mountains were researched using the methods of maximum value composite, trend line analysis and correlation analysis as well as averaging method. The results showed that the vegetation coverage in the Qilian Mountains increased gradually from the west to the east, and it in the eastern part of the Qilian Mountains was higher than that in the western part. There were some significant spatial differences of vegetation coverage change, for example, it increased in the central and western parts of the Qilian Mountains, but decreased in the eastern part. The area with an increase of vegetation coverage was 79 149 km2 and accounted for 52.93% of the total area investigated in the Qilian Mountains, and the area with a decrease of that was 22 865 km2 and accounted for 11.09％ of the total. The vegetation coverage was in a significant increase trend in recent 10 years, and the monthly vegetation coverage in growth season was also in an increase trend. The increase of vegetation coverage in the Qilian Mountains was caused by the increase of precipitation under global warming. There were the significant correlations between NDVI and temperature and precipitation, and there was also a time lag in their changes. There was a significant correlation between the NDVI in June and July and the precipitation in previous one month and two months, and their correlation coefficients were 0.788 and 0.684, respectively; there was an extremely significant correlation between the NDVI in August and September and the temperature in the same month and previous one month, and their correlation coefficients were 0.825 and 0.829, respectively.

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