Water problem is the most serious natural resource and environmental problems of the 21st century.Ecological imbalance which dues to shortage of water resources, soil erosion, and mismanagement of water resources affects survival of human beings, especially in add and semi-arid regions, Western China.Studying ecological water demand in the region contributes to help understand the severity of ecological imbalance.Because of the restriction from natural conditions of arid and semiarid regions, it is difficult to obtain sufficient observed meteorological and hydrological data.Therefore it is impossible to study ecological water demand in fiver basin scale only depending on observed meteorological and hydrological data.