the primary drinking water source to further solve the drinking water problems of these villages, so as to completely eliminate endemic fluorosis in the region.

The coupling relationship between rivers which contain high concentration of fluoride ions formed by the convergence of groundwater and precipitation and endemic fluorosis of subregion in northwest China is less studied at home and abroad. Based on the historical 40 years data on endemic fluorosis and the spatial distribution and formation mechanism of high concentrations of fluoride in Qingshui River basin in Ningxia, this study concludes that there is a close coupling relationship in south-central Ningxia between the endemic areas of endemic fluorosis and the spatial and temporal distribution of excess fluorine water of Qingshui River basin. This relationship indicates that fluoride in the groundwaterof the Qingshui River basin has long been affected by geological structures, low-lying and closed terrain, and drought. Qingshui River and shallow groundwater in the basin have a strong process of mutual resupply and transformation. And we consider the phreatic aquifer of the basin as the prominent contributor for endemic fluorosis because shallow groundwater is the main source of drinking water for a long time in this region. The temporal and spatial distribution of regional endemic fluorosis with long time series and its corresponding relation with water fluoride content in watershed were discussed. Then, we preliminarily concluded that the upper part of the basin is the high-incidence areas, and the middle and lower reaches are the middle and lower levels. The spatial distribution of villages and population of