Understanding potential evapotranspiration (PET) is essential in planning economic uses of water resource and in assessing the potential ecological conditions for ecological restoration. In the semi-arid western Chinese Loess Plateau. This work tested three models commonly used to estimate monthly PET rate (i.e. Behnk-Maxey, Prestley-Taylor and Hargreaves). The major purposes are: (1) to determine the model used to calculate PET with small data requirements and high accuracy in the Zuli River Basin; and (2) to calculate the areal distribution of potential evapo-transpiration in the study area. From the approach, conclusion can be drawn that Hargreaves model may be the best way to estimate PET in the semi-arid area of the Loess Plateau with sparsity of weather stations. The general methods described here are expected to be applicable to the entire Loess Plateau.