The processes of energy and water exchange between the earth surface and atmosphere have a very significant influence on the microclimatic conditions and consequently, on plant production. Evapotranspiration is one of the most important processes that connect energy and water balance of a cultivated field with plant growth. This paper compares the results of simulations and measurements of evapotranspiration from the cultivated fields in Middle Europe. The modelling system THESEUS was used in this study. Evapotranspiration was also calculated from the latent heat flux density (LE) measured by the use of a modified Bowen’s ratio method. The models, as well as the modification of the Bowen’s ratio procedure are described. Heat balance components for 8 measuring sessions (81 days) were used in the comparison. There was a good agreement between model simulations and measurements. The average relative error in the evapotranspiration estimation by the model was about 5% for one month or longer integration period.