Abstract: This paper analyzes the influence of reduced irrigation on water balance of farmland by the soil-water-atmosphere-plant(SWAP)Model.The experiment site is an area controlled by lateral canal in Hetao irrigation district of China.The results show that the ratio of evapotranspiration to total consumed water is over 90%,which further proves evapotranspiration is the leading water-consumed factor in Hetao irrigation district.The result also shows that relative production will fall evidently due to reduced irrigation water.Therefore,when the quantity of water alloted in Hetao irrigation district is cut down from 5.2 billion m³ to 4.0 billion m³,the pattern of crops and irrigation scheduling etc must be regulated newly.