Meteorological data show that air temperature and precipitation have changed greatly in Northwest China during the past half century. The climate change, combined with human activities with large-scale and high intensity, leads to change in vegetation. Since climate is the major driving factor to vegetation changing, the study of spatial and temporal changes of vegetation due to climatic variation should be carried out in Northwest China, an extremely vulnerable region in ecology and environment. Meteorological and NDVI time series datasets from 1981 to 2006 and other geographic data were used to reveal the spatial and temporal variations of vegetation in the arid regions of Northwest China. It is found that (1) NDVI and vegetation area have increased 3.2% and 4.5%, respectively, in the last 26 years. And a lengthening of growing season and a delaying autumn has taken place; (2) Vegetation area had a significant increase before 2000, but followed by a decreasing after that, such as NDVI and vegetation area in the Yili River Valley, the Middle Tianshan Mountains and the plain regions had significantly decreased while in the upper reaches of rivers and mountain areas had increased; (3) For the interannual variation, between the NDVI and air temperature and precipitation have no obvious correlation in most regions of Northwest China. However, in the areas where the annual temperature is lower than 4.58 ℃, between NDVI and annual temperature shows a positive correlation; moreover, in the areas where the annual precipitation is higher than 180 mm, between NDVI and precipitation also has a positive correlation; (4) Between NDVI and temperature there is a strong correlation in spring and summer, while between NDVI and precipitation there is a strong correlation in fall; (5) Since 2000, the vegetation cover and NDVI values have decreased, associating with air temperature rising and declining of precipitation increasing rate.