【Objective】 The study aimed to clarify the relationship between vegetation cover and its driving factors to provide basis for the sustainable development of ecological environment and scientific estimation of climate change impacts on vegetation pattern in source areas of the Yellow River.【Method】Based on SPOT VGT-NDVI (normalized difference vegetation index) data and the ITPCAS forcing dataset (reanalysis datasets), trend analysis, the Mann-Kendall statistical method, R/S analysis and correlation analysis were used to investigated the spatiotemporal changes of NDVI and climate factors during 1999 - 2015. The effects of temperature,precipitation and Rn(surface net radiation) and human activities on vegetation cover change were also analyzed.【Result】(1) The NDVI in source region of the Yellow River was high in the southeast and low in the northwest. The NDVI has been increasing with an average rate of 1.6% per 10 years from 1999 to 2015. The area with increasing trend accounted for 78.2% of the study area. There existed abrupt point in around 2003. Temperature and precipitation were on an upward oscillation trend during the same period,while Rn was opposite. The trend of NDVI and meteorological factors would continue in future. (2) The annual NDVI had significant positive correlation with temperature,insignificant positive correlation with precipitation, and insignificant negative correlation with Rn. The correlation between NDVI and annual temperature was best in partial correlation analysis. (3) The responses of NDVI to temperature and precipitation lagged by one month, while the response to Rn lagged by two months.【Conclusion】 The ITPCAS forcing dataset had good applicability in source region of the Yellow River. In both annual and monthly scales, temperature was the most important meteorological factor influencing vegetation growth,and the increased NDVI was mainly attributed to climate warming and the implementation of comprehensive ecological protection project.