Abstract: In order to analysis the influence of water deficit on crop production, the characteristics of the crop water sensitive index in crop-water production function model and its cumulative curve were analyzed, and widely used cumulative function of crop water sensitive index was improved. The improved cumulative function had little differences of the former one during the middle growth stage, but the differences were significant in the early and late growth stage. The improved cumulative function could be used to simulate the changes of cumulative value of crop water sensitive index during the whole growth stage continuously. The improvement was verified by crop production and evapotranspiration data from deficit irrigation experiments of winter wheat in Xiaohe of Shanxi Province and late paddy rice in Guilin of Guangxi Province. The simulated cumulative value of crop water sensitive index using the improved function accord well with the measure value, its have better simulation effect than the former function.