Changes of relative humidity and vegetation coverage in Weihe River basin were studied and the effects of vegetation restoration on air relative humidity were analyzed quantitatively by using GIS, remote sensing technology and statistical methods.It was observed that:(1)The relative humidity had a latitude zonal distribution character, increased from north to south. The overall average relative humidity of Weihe River basin declined gradually and presented an upward trend during the last 10 years. (2)The overall vegetation coverage was improved, while the local vegetation coverage presented a bad trend. Nearly a third of basin was stable .Counties(cities) with an obviously improving trend were mainly located along the main stream as well as in the upper reaches of Jinghe River and Malian River and the middle reaches of Beiluo River. Counties(cities) with a degrading trend were mainly located in the middle and lower reaches of Weihe River and the middle and the upper rea-ches of Jinghe River. (3)Before the implementation of vegetation restoration, the main influence factors were precipitation, sunshine and temperature. After the implementation of vegetation restoration, the rela-tive humidity increased or decreased with the vegetation cover condition improving or degrading. (4)The NDVI in Wuqi County was negatively correlated with the winter relative humidity and yearly averaged rela-tive humidity. There was a significant positive correlation between the NDVI and the relative humidity in spring and summer. During the period from 1982to 2006, vegetation condition in summer had the same trendas relative humidity.Vegetation condition was better or worse when relative humidity was high or low.