The limited water supply irrigation system for soybean crops in Shanxi Province was studied. The irrigation data of Limin experimental station in Linfen City, Shanxi Province had been selected. Frequency calculation of rainfall data of Limin was made, choosing 2010, 1993 and 1997 respectively as the sample year of plain water year (50%), water year dry year (75%) and special drought year (95%) of Limin. The Jensen model as the basis for calculation was selected, calculating the actual yield value of crop according to the actual crop water requirement, crop maximum water demand, sensitive index value and maximum crop yield at each stage. Through the selection of the number of days of irrigation, the optimization model of irrigation times was established. The limiting condition is the maximum actual yield. The quota irrigation system of soybean crops in different hydrological years was determined. According to calculation results, each target year was three times, with the highest amount of water.