On the basis of 1500 grids of 0. 25°×0. 25°, the VIC(Variable Infiltration Capacity)-3L model was applied to calculate the hydrologic process in the Yellow River River Basin from 1961 to 2012, getting daily actual evapotranspiration(E)and potential evapotranspiration(E_P). Then the Mann-Kendall trend test method and the Budyko water-energy balance formula were applied in analyzing the variational trends of E, E_P, Evapotranspiration ratio(E/P), dryness index(E/E_P), and the influence of water and energy supply on evapotranspiration. The results show that E and E_P have a tendency of decreasing on the whole, and E_P shows a remarkable trend with spatially variety. The evapotranspiration ratio(E/P)and dryness index(E/E_P)do not show obvious change. Evapotranspiration in the upper reaches of the Yellow River Basin was mainly affected by the limitation of energy supply, while the one in the middle and lower reaches of the Yellow River Basin was affected by the limitation of water supply.