Abstract: For simplifying the calculation of actual evapotranspiration in cropped field, the soil moisture of the depth from 0 to 300 cm in the maize field and the meteorological observational data in 1999 at Dingxin county in Hebei Province, where is an agrometeorological experiment base of Chinese Academy of Meteorological Sciences, and the soil moisture of the depth from 0 to 50 cm and the meteorological observational data at 5 stations in North China from 1991 to 1995 are used. The possibility that actual evapotranspiration in the maize field is calculated by using a simple reference evapotranspiration model is examined. Prisetley-Taylor modeland FAO Penman-Mentaith (1998) model are compared and the factors impacting on evapotranspiration are discussed. Based on the experimental data and using leaf area coefficient and mean soil relative moisture as the model factors. A formula calculating actual evapotranspiration is made. Evapotranspiration is calculated by this formula, and the soil moisture of the depth from 0 to 50 cm and the meteorological observational data at 8 stations from 1999 to 2000 are applied to validate. The average errors are in the range from 10% to 15% generally.