The Loess Plateau of Gansu Province is located in semi-arid and semi-humid transition zone. The accurate estimation of potential evapotranspiration is one of the main works in assessment of water resources. Based on the meteorological data at Xifeng National Base Climate Station in 1961—2006,5 kinds of model for calculating potential evapotranspiration widely used in semi-arid area are chosen for the evaluation with reference of evaporation. The FAO Penman—Monteith (1998) model has a significant relevance,small standard deviation with evaporation,and the high stability and is the most suitable model for calculating the potential evapotranspiration. The next suitable model is the FAO PPP—17 model. The Hargreaves model has the advantages of fewer climatic factors,convenient use,and higher accuracy over other models in estimating potential evapotranspiration. It is demonstrated that the Priestley—Taylor model has some reference values in calculating evapotranspiration,but the model shows a low relevance level with evaporation. Therefore,the model should be modified before it is put into use. The association between calculated value of the 24Radiation model and evaporation dose not reach the level of assumption checking in summer and thus its use is limited. The model should not be used in research work in the Loess Plateau of Gansu province.