In arid and semi-arid regions, irrigation system optimization is very significant for rational water use. The optimized irrigation system of cotton in yuncheng district of shanxin, potatoes in Datong district was researched. By using Jensen model, with the goal of maximizing the benefit, the yield and benefit were calculated. The results showd that the water consumption of different economic crops was different, and the irrigation times under the condition of the maximum yield benefit was also different. Water demand of cotton was larger, in normal year. The irrigation water was 375 mm, irrigation times was 5, the Yield was 2250 kg/ha, under the condition of the maximum beneft. The irrigation water is 150 mm, irrigation times was 2, the Yield was 23925 kg/ha, under the condition of the maximum beneft. Water demand of potatoes was smaller. The irrigation water was 75 mm, irrigation times was 5, the Yield was 17626 kg/ha, under the condition of the maximum beneft.