Abstract: The purpose of this paper is to examine the water deficit in Xi'an area,the ancient city in China.This paper analyzes the hydrologic characteristic of surface water in Xi'an area by the monthly flow time delay curve and the transcendental probability curve,and evaluates the water supply level in Xi'an city with the water-supply guaranteed rate and the shortage index as the evaluating index,through the joint operations among the reservoirs and the operation without reservoir.The results show that the needs of the present water can not be met without the reservoir operation in Xi'an city,and the mean annual surplus water will still reach 200 million m³ in 2030 with the joint operation among the three reservoirs,which proves that the water resource developing is still of certain potential.