This study constructed growing season NDVI in 1981-2010 based on GIMMS NDVI and MODIS NDVI data in Inner Mongolia. The characteristics of NDVI change were analyzed and natural and human influencing factors were investigated in each county (banner) by trend analysis and multiple regression analysis. The results indicate that NDVI changes in Inner Mongolia showed great heterogeneity. The regions that experienced significantly increased vegetation cover were mainly distributed in Erdos City and Alashan Prefecture in southwestern and Tongliao City in eastern Inner Mongolia, and the regions that experienced significantly decreased vegetation cover were in HulunBuir and Xilinguole Prefectures in northern Inner Mongolia. For the increased vegetation cover regions, human activities were the dominant factor, and climate change played the second role; the coupling of climate change and human activities also had certain impact on the vegetation increase. The increase of the rainfall, implementation of banned grazing policies and increase of cropping area were the main factors driving the increase of vegetation. However, for the decreased vegetation cover regions, the role of human activities was slightly greater than that of climate change. The reduction of rainfall in the central and eastern Inner Mongolia and the raise of wind speed in some counties in nearly 10 years were the main climatic factors driving the significant decrease of vegetation. Although afforestation and the increase of cropping area might lead to the increase of vegetation cover at local scale, it was not enough to counteract the adverse effects of drought on vegetation growth at county scale; nevertheless, it might lead to regional vegetation degradation.