Abstract: In order to obtain the proper calculation methods for reference crop evapotranspiration (ET0) in Hetao Irrigation District in Inner Mongolia and based on the micrometeorological data, four calculation methods (Priestly-Taylor. FAO Penman, Hargreaves-Samani, Irmark-Allen)　for ET0 were compared with FAO56 Penman-Monteith, respectively, and their applicabilities in Hetao Irrigation District were evaluated. The results show that calculation results of FAO Penman method is closest with FAO56 Penman-Monteith, The average absolute error and average relative error are 0.43 mm/d and 12.50%, respectively. Other methods have different positive and negative deviations in different seasons. In the total calculation periods, deviations between the results by Irmark-Allen, Hargreaves-Samani and Penman-Monteith method are larger, so they can not be used in the district for its weather conditions. the results by FAO Penman method are similar with FAO56 Penman-Monteith method and they can be applied to the most kinds of climate condition. Hargreaves-Samani method can be used in the district in which the difference in temperature is smaller. Irmark-Allen and Priestley-Taylor methods can be used in the area in which the relative humidity is larger.