Using the meteorological data, vegetation distribution data, water resources data, we calculated the minimum and appropriate ecological water requirement of existent forest and grassland in growing season in the Central and Southern Ningxia Hui Autonomous Region. Through the analysis of equilibrium between the eco-environment water demand and rainfall resource, the results showed that in Longde County and Jingyuan County, which locate in the south area, with an average rainfall of 350~550 mm, the minimum and appropriate ecological water requirement both can be met by precipitation, and the vegetation grow well. In Pengyang County and Yuanzhou County, which locate in the south area, with an average annual rainfall of 350 mm or so, the minimum eco-water demand can be satisfied, but appropriate ecological water demand cannot be met. So reasonable grass planting structure should be considered in the area. In Haiyuan, Yanchi and Tongxin Counties in the central arid area and Xiji County in the south area, with an average annually rainfall between 175 and 280 mm, both minimum and appropriate ecological water demand can not be met, it is unreasonable to develop forest and grassland in this area.