Abstract: Aiming at the problems of environment and lacking of water resources in arid and semi-arid region. Based on the idea of system analysis and constructing regional water resources optimal allocation model for environment and water saving, on one hand, a method of water resources calculation considering water saving, water right and environment was put forward; on the other hand, the reasonable method of water resources optimal allocation was given. At the present, and the year of 2010 and 2030, the water resources can be supplied is 5.6415×10⁷, 5.7967×10⁷ and 5.6572×10⁷ m³, and the quantity of scarcity is 1.5446×10⁷, 2.1003×10⁷, and 3.6279×10⁷ m³, respectively, the result provides a basis for the planning and designing of the region.