Evapotranspiration is a key element of the water cycle, and analyzing its variations helps understand the spatiotemporal distribution patterns of regional water resources. The water source conservation area of the Yellow River Basin is an important ecological function area in the Yellow River Basin. Studying the characteristics of evapotranspiration changes in this area and conducting attribution analysis can help alleviate the water supply-demand contradictions in the Yellow River Basin. Based on machine learning and the ERA5-land reanalysis dataset, this study explored the spatiotemporal variations and influencing factors of evapotranspiration in the Yellow River water source conservation area from 2000 to 2022. The driving factor regression analysis method is used to analyze the influence of different factors in different regions. The results show that: (1) The multi-year average distribution range of evapotranspiration in the Yellow River water source conservation area is 256.49-841.45 mm, with a spatial distribution characteristic of decreasing from east to west and an overall increasing trend. (2) The main influencing factors of evapotranspiration in the Yellow River water source conservation area are surface net solar radiation, total precipitation, and relative humidity. The dominant influencing factors vary in different sub-basins and are related to the hydrothermal conditions and underlying surface conditions in the region. (3) The ERA5-land reanalysis dataset has good simulation accuracy and can serve as a data source for large spatial scale and long-time interval studies. However, due to the complexity of the underlying surface, adaptive assessment within the study area is still needed.