Accurately quantifying of hydraulic lift (HL) and its eco-hydrological effects has great significance for the terrestrial ecosystem water cycle and global change research. Based on measurements of the soil water content and latent heat flux by the eddy covariance method during 2011-2012 in the lower Heihe River, the HL was first calculated by separated water depletion (WD) in the soil water content. Its contribution to evapotranspiration (ET), that calculated from latent heat flux, was then determined. The daily variation of HL that largely occurred in 20-60 cm soil depth ranged from 0 to 1.4 mm/d with an average of 0.22 mm/d, and the WD was from 0 to 0.76 mm/d with an average of 0.23 mm/d. The annual variation of HL and WD was synchronized and the magnitude of both was in positive balance, indicating that the water extracted from the deep soil layer or groundwater via HL was expected to meet the transpiration; however, the remainder of the water was retained in the soil layer. The daily variation of ET ranged from 0.31 to 6.42 mm/d with an average of 3.37 mm/d; however, the annual variation of HL and ET has a time-lag effect, with the maximum of HL and ET occurring in May and July, respectively. The ratio of HL to ET ranged from 0.06% to 108.25% with an average of 19.25%, which indicated that the HL did not increase with an increase in ET. Two possible reasons for this are that the HL was restrained by the low soil water moisture of the deep layer or by the nocturnal transpiration during the dry season. Further research is required to confirm which one of these is correct.