Abstract: High salinity groundwater is widely and unevenly distributed in northeast Ningdong Coalfield of Ningxia Hui Autonomous Region, and it varies greatly throughout the coalfield. This paper studies the distribution characteristics and formation mechanism of high salinity groundwater. Firstly, spatial distribution characteristics of high salinity groundwater was researched, and then, Piper trilinear graph, Gibbs graph and ion proportionality coefficient were used to investigate the formation mechanism of high salinity groundwater. The results show that groundwater salinity value varies from 0.30 g/L to 23.56 g/L, and the average value is 5.84 g/L. The proportions of fresh water, brackish water, salt water and salt water are 3.16%, 50.00%, 33.68%, 13.16% respectively. In the horizontal direction, the salinity of bedrock fissure water decreases gradually from east to west, and a high salinity anomaly zone is formed in the south of Yuanyang Lake mining area. In addition, high salinity anomaly zones occur in scattered areas of the west, north and south of the coalfield. The high salinity is related to the dissolution of gypsum, salt rock and pyrite and the long-term retention of groundwater. The mineralization gradually decreases from east to west due to the influence of the Ordos thrust nappe structure. However, Yuanyang Lake mining area is located in the transition zone of the south and north thrust systems of Ordos platform, with relatively complete folds and relatively closed groundwater environment. Thus, groundwater salinity is particularly higher than other area. In the vertical direction, from aquiferⅠ to aquiferⅤ, the groundwater salinity increase gradually. This is mainly related to the slow closure and regeneration of deep groundwater environment. The research will provide theoretical basis for the development and utilization of underground resources in Ningdong Coalfield and similar mining areas.