Abstract: Based on the microclimatological data the daily evapotranspiration in the field of winter wheat during the period of heading and milky maturity is preliminarily calculated with the help of the Penman formulas and the other methods, such as energy balance, Bowen ratio and aero-dynamics. The modification of Penman formula is principally considered. The accuracy and error analysis of the formulas and methods above are evaluated by the results of water balance method, which can be regarded as a standard. The conclusions show that after being modified by the crop coefficient water content and heat exchange in soil as well as the surface temperature of evaporation. Penman formula can be used to calculate accurately the daily evapotranspiration of cropcovered field on the conditions of different energy and water supply