Abstract: Based on the experiments of spring wheat and the relationships between soil moisture，weather condition and crops，the moisture indexes and the water requirement of spring wheat in different growth stages are determ ined by using the equation of soil moisture balance in farm land and the method of evapotranspiration calculation which is offered by FAO ．The relative equation between soil moisture and physiology and ecology of spring wheat is established using the method of curvilinear simulation．Finally，a model of saving water，as well as the amount and the irrigation frequency of spring wheat in irrigated areas is established．