Based on the theoritical analysis and the measured data in corn-land, this paper pre-sents a model to forecast soil water dynamic process in corn-land. The model includes threebranch systems, they are soil water dynamic process in root zone of corn, dynamic process ofwater uptake by corn root, and dynamic process of evapotranspiration. The measuring and es-timating method of parameters in the model is also described. The result of application showsthat the forecast of soil water dynamics and evapotranspirat...