Land surface evapotranspiration has an important impact on the simulation of earth’s hydrological processes and hydrological balance， especially in the arid and semi-arid regions. Where the heterogeneous land surface conditions pose new challenges to the simulation of evapotranspiration using the remote sensing models. In this paper， the satellite data collected from Landsat and MODIS were used as driving data of TSEB model， respectively， to obtain the temporal and spatial distribution pattern of land surface evapotranspiration in the downstream of the Heihe watershed. Then the surface heat fluxes measured by the large aperture scintillator with a source area of several kilometers and the eddy covariance with a source area of several hundred meters were used to evaluate the model outputs at the multiple spatial scales. The results showed that the TSEB estimated surface sensible heat flux using Landsat and MODIS data is comparable with the observations from the large aperture scintillator， with Root Mean Square Error （RMSE）values of 48.47 W/m2 and 58.57W/m2， respectively. While comparing with the observation of eddy covariance， the Landsat data-driven TSEB estimates produced RMSE value of 89.37W/m2. Therefore， it can conclude that the TSEB model has a better agreement with ground measurements when using the finer satellite remote sensing data as model inputs. In addition， large aperture scintillator observation with a source area of several kilometers can partially solve the spatial mismatch issues between the remote sensing products and the ground measurements.