The current situation of urgent requirement and obstacles in retrieving land surface evapotranspiration (ET) operationally were analyzed. By the comparison of the most commonly and widely used models for ET estimation, taking into account for the principles of independence, simplicity, versatility, scalability for operational retrieving, and selecting the Priestley-Taylor(PT) model as the key algorithm,,an operational technical flow-scheme was established to obtain the daily ET. With the support of MODIS data and meteorological data, taking Heihe river basin as experiment area, the model and flow-scheme were verified, and daily ET were retrieved. Evaluation of the relative accuracy of operational ET estimation flow-scheme was made by using FAO56 Penman–Monteith model supposed to be the standard model. High correlation coefficients of 0.880 were observed by these two models. Results with relatively high accuracy proved that the PT model and the flow-scheme were workable, and sufficient to satisfy the requirement of operational processing, and it was worthwhile to utilize them for the future operational ET retrieving.