Abstract: This paper presented a method to evaluate vegetation degradation in semi-arid and semihumid region.Based on eliminating irrigation land,we estimated the potential vegetation index by imitating the upper borderline of scatter plots in NDVI-climate variables feature space and appraised the vegetation degradation through comparing actual vegetation index with potential vegetation index.The degree of vegetation degradation takes on prominent spatial difference.On the whole,the degree of vegetation degradation is the most severe in the middle and the east of Gansu Province and the south of Ningxia autonomous region.NDVI tend to saturation where climate is more humider and so the evaluating result has some uncertainty.