Abstract: In order to estimate irrigation water-saving potential, this paper proposed a new theory and method based on irrigation district scale. According to this theory, the conception of “gross water-saving” and “net water-saving” were introduced to avoid the argument of opinions between engineering-type water-saving and real water-saving. Furthermore, the assessment indicators of irrigation water-saving was conducted and the calculating model of water-saving potential was proposed. To verify this theory and method, a case study on Tuhaimajiahe river basin was made to estimate water saving of irrigation engineering measures with two scenarios at 20% and 40% water-saving rate seperately. The estimate result showed that the water-saving irrigation projects had good effect on gross water-saving water than on net water-saving.