Abstract: This paper calculates the actual and potential evaportranspiration of wheat based on the field water balance. furthermore,the sensitive index of Jensen's water production function model is analyzed. the result shows that the sensitive index is related to the growing stage duration of the crop and the ratio of each stage to the whole growing period. The accumulated sensitive index of each grow stage after green can be expressed as a function of time,but it is not related to the stage devision. Sensitive index of each stage can be easily calculated from the stage deviion. Sensitive index of each stage can be easily calculated from the function. The result also shows that the relation between crop water consumption and crop yield can be expressed by the jensen's model quite well.