The areal data for each type of natural vegetation in 1987, 2000 and 2010 in the Shiyang River Basin were obtained using remote sensing method with the aid of ArcGIS 9.3 software statistics. Accordingly, the ecological water requirements of natural vegetation in different counties and areas of the basin were estimated. By using Avi Lubyanka estimation method, it turned out that the suitable ecological water requirements for natural vegetation was 2.43, 2.34, 2.06 billion m³ in 1987, 2000 and 2010, respectively. The counties, in order of decreasing water requirement, were Sunan County, Tianzhu County, Yongchang County, Minqin County, Gulang County, Liangzhou area and Jinchuan area. The ecological water requirement for each of woodland and grassland in the basin basically took up half the total water demand. However, it is obvious that there was a sharply different percentage for the ecological water requirements of woodland and grassland in different areas, and the water using efficiencies of natural vegetation were between 2.74 and 16.55 kg/(hm²·mm). Through the study of the ecological water requirements of nature vegetation in three different periods, it is found that the water requirement of nature vegetation showed a decreasing trend both in the total water requirement and the coverage degree of natural vegetation. So the determination of the suitable ecological water requirement for natural vegetation has a significant meaning to the rational allocation of water resources and the scientific schemes worked out for ecological restoration.