Abstract: This paper analyzed the trend of vegetation variation and its influencing factors in Northern Shaanxi Province，China since the implementation of the ecological building in 1999，based on NDVI （MODIS 13Q1），meteorological and statistical data. Correlation analysis and SLOPE approaches were used to detect the trend and to estimate amplitude of NDVI changes，and a regression method was used to analyze the relationship between [NDVI] change and rainfall，temperature and afforestation area. ArcGIS was used to map the spatial variation of the NDVI and its change trend. The results showed that in most parts of Northern Shaanxi，i.e. 72.58% of the total area，the vegetation was obviously improved during 2000-2011，in terms of [NDVI] changes at the 0.05 significance level. This improvement was most evident in the hilly and gully loess area，the key implementation area of the ecological building. In 27.18% of the study area，the NDVI had no significant change during the period，which mainly included forest vegetation in southern Ziwu and Huanglong Mountain areas，and a small part of grassland in Yulin and Dingbian. In a small area （0.24%） of the region，the [NDVI] showed an apparent decline trend，due to the land converted to urban and mining & industry land use. Among regions covered with different vegetation types，the region formerly cultivated for growing crops had most evident increase in the NDVI，increasing by 24.90% （0.122 3），with the amplitude （SLOPE value） of 0.014 3 during 2000-2011. The area covered by grass vegetation also had an apparent increase，increased by 23.15% （0.101 4） in NDVI with the SLOPE value of 0.011 8. The lowest increase appeared in the area covered by forest vegetation，where the NDVI increased only 5.56% （0.045 0） and the SLOPE value was 0.005 0. In the shrub and desert regions，the NDVI increased 10.48% （0.074 5） and 14.84% （0.068 3），respectively. Two representative regions were selected，i.e. Yan’an City with significant NDVI changes，and Dingbian County with non-significant [NDVI] changes，and conducted regression analyses to check possible effects of rainfall and temperature changes on the NDVI variation. It was found that the annual NDVI values were not correlated with the annual precipitation and temperature （R²<0.15） during 2000-2011. But regression analyses between changes in the mean regional NDVI and afforestation area for 25 counties in the study area，revealed a significant correlation （R²=0.561）. These regression results illustrated that the ecological building typified by returning the sloping farmland to forestland/grassland was the main factor affecting the NDVI change during 2000-2011 in northern Shaanxi Province，while precipitation and temperature had no or only a minor contribution to the change. In general，the spatial NDVI variation was in accordance with the distribution of the afforestation. It can be concluded that the ecological building implemented in 1999 have been an apparent positive effect on the environment，which greatly promoted the vegetation restoration in Northern Shaanxi Province.

Key words: NDVI,  , ecological building, Northern Shaanxi province