Based on infrared information under the condition that crop canopy surface is not always in satura-tion, this paper presents a model for estimating the crop waer deficiency. The physical concept of themodel is clear and definite, and it is convenient to calculate the crop water stress index (F). The roleof environmental factors such as the net radiation, the windspeed, etc. played on the model and thephysical meaning of the model are expounded in this paper. The model links up Jackson’s heat balancemethod and Idso’s graphic solution method. The model was tested and verified by the data acquired fromYucheng experimental station in Shangdong Province. Throughout the wheat growing season the totalcorrelation coefficient between daily crop water stress index (F) and dai1y soil water content is -0.85.During each growing stage, the correlation coefficients between average crop water stress index (F) inthe stages and average soil water content in the stages are, respectively, -0.91 for jointing stage, -0.99for Based on infrared information under the condition that crop canopy surface is not always in satura-tion, this paper presents a model for estimating the crop waer deficiency. The physical concept of themodel is clear and definite, and it is convenient to calculate the crop water stress factor (F). The roleof environmental factors such as the net radiation, the windspeed, etc. played on the model and the physical meaning of the model are expounded in this paper. The model links up Jackson’s heat balancemethod and Idso’s graphic solution method. The model was tested and verified by the data acquired from Yucheng experimental station in Shangdong Province. Throughout the wheat growing season the totalcorrelation coefficient between daily crop water stress index (F) and dai1y soil water content is -0.85.During each growing stage, the correlation coefficients between average crop water stress index (F) inthe stages and average soil water content in the stages are, respectively, -0.91 for jointi ng stage, -0.99for