Water resources exploitation and sustaining development of arid and semi arid area is one of the most important global environment problems.1/3 of the total earth surface is arid or semi arid,and in China,it is 47.5%.Among it,the arid area with precipitation less than 200mm/a is 26.6% of the total area of China.Water system in arid area has the following characters:total water resources shortage,poor recharges,distribution unbalance,evaporation playing a key role in water cycle,river and connected aquifers forming a unity system,shallow groundwater having certain present recharge but deep groundwater usually no with very low tritium detected. A series of environment deterioration problems,such as desertization,salinization of soil and salinization of groundwater,have risen during water resources exploitation because ecosystem is rather weak.To realize the reasonable utilization of water resoures in arid area,we need to manage water resources in scope of catchment,to optimally use surface water and groundwater in conjunction,to evaluate the capacity of water system and control the development of the oases,to keep reasonable ecosystem water level and demand and to construct water saving society in arid area.