To study the distribution characteristics and causes of underground brackish water in the plain area of the Hotan River Basin, and to improve the utilization efficiency of unconventional water sources (brackish water) in arid areas, by collecting 114 sets of groundwater samples, a comprehensive analysis of the chemical characteristics and genesis of brackish water was conducted using methods such as mathematical statistics, correlation analysis, and hydrogeochemistry. The results show that the overall distribution of brackish water in the study area is in a strip shape from south to north, with an area of 4124.18 km², accounting for 38.76% of the total area. It is mainly distributed near the oasis desert transition zone and the middle and lower reaches of the fine soil plain area. The hydrochemical types are mainly Cl·SO₄-Na·Ca, Cl·SO₄-Na·Mg, Cl·SO₄-Na, Cl-Na·Ca, Cl-Na·Mg, and Cl-Na. The development and utilization of groundwater did not have a significant impact on its distribution characteristics. The potential for the development of brackish water is greater in the areas near the oasis edge and far from the river channel. The controlling factors for the formation of brackish water in the watershed are ranked as follows: evaporation and concentration>water rock interaction>cation exchange. In the alluvial plain area in front of the mountain, both water rock interaction and cation exchange are significant. In the middle and lower reaches of the fine soil plain area, the influence of water rock interaction is much higher than that of cation exchange, and the dissolution of rock salt dominates in the water rock interaction. The research conclusion has important practical significance for the zoning and rational development of unconventional water sources in the Hotan River Basin.