Vegetation is a crucial ecosystem component in the ecologically fragile and typically human-disturbed Loess Plateau. The Loess Plateau has undergone dramatic vegetation changes in the past few decades due to dramatic human activity and climate change. It is essential to clarify the characteristics and mechanism of vegetation variation for future ecosystem restoration and conservation. Based on the long-term data record (LTDR) NDVI dataset, this study employed scenario reconstruction and target pixel determination to explore a new insight and provide a clear finding on vegetation-climate interactions, and then give a reliable detection and assessment on vegetation variation, as well as the impact mode and intensity. The results show that NDVI of the three vegetation types was positively correlated with precipitation, especially cropland. The vegetation conversions significantly impact NDVI, particularly the conversions from cropland and grassland to woodland. Attribution analysis reveals that climate change and human activity jointly affect the variation of NDVI, but the leading role changed around 1999. During 1981-1999, 78% of the Loess Plateau experienced a declining NDVI, which was mainly caused by climate change. Conversely, NDVI increased in 47% of the area after 2000, particularly in the central and northern regions. Positive anthropogenic contribution was detected in over 49% of the area. This study is expected to provide the basis for developing effective and adaptive strategies to realize the economic and ecological stability of the Loess Plateau.