Based on the two-source energy balance(TSEB) model, the spatiotemporal variations of evapotranspiration(ET), plant transpiration, and soil evaporation were simulated on the Loess Plateau from 2000 to 2020. The response mechanisms of evapotranspiration and its components to climate and underlying surface changes were revealed using methods such as ridge regression and residual analysis. The results indicated that the interannual increasing rate of ET on the Loess Plateau during the study period was 9.25 mm/a, and the interannual increasing rate of plant transpiration was 9.42 mm/a. Changes in climate and vegetation, along with nonvegetation underlying surfaces, dominated the increase in evapotranspiration and plant transpiration, with the main controlling factors were the leaf area index(LAT), temperature, and precipitation. The interannual decreasing rate of soil evaporation was -0.35 mm/a, with the combined effects of climate and vegetation changes and non vegetation underlying surfaces change, and the main controlling factors were LAI, precipitation, temperature and wind speed. Climate change is the most significant driving factor affecting evapotranspiration and its components on the Loess Plateau, followed by vegetation changes, while changes in non vegetated underlying surfaces have the least impact.