Abstract: The contrast between water resource supply and demand is very prominent in the arid and semiarid inland basins of Northwest China. The plain area of those basins is arid,the groundwater is mainly formed in the mountains and their piedmont areas,and originate from the atmospheric precipitation and ice/snow melt water. Groundwater undergoes multiple hydro-chemical processes during the long-distance runoff before discharging from the aquifer,which determines the complexity of the formation and evolution of groundwater hydrochemistry in arid and semiarid basins. The hydro-chemical evolution of groundwater is the main factor affecting its chemical composition and content,and is also the internal mechanism controlling its quality. Therefore,the understanding of the evolution mechanism of hydro-geochemistry is of importance for the scientific management of regional groundwater resources,and is beneficial to coordinated development of the ecological environment and the economy in arid areas. In this study,the groundwater flow system of the northern Tacheng Basin is taken as the research area. The water–rock interactions that occur through groundwater flow are analyzed quantitatively by using inverse modeling based on selecting typical groundwater flow paths,identifying the potential mineral phases and reaction directions involved in hydro-geochemical processes,and calculating the evaporation degree of groundwater. Results reveal that water–rock interactions play a dominant role in the hydrochemical evolution of unconfined groundwater,while evaporation has little impact on its hydro-chemical composition. Dissolution of gypsum,halite,and dolomite,positive cation exchange between Na+-Ca2+,minor plagioclase dissolution,and calcite precipitation occur in the groundwater system flowing from the recharge area to the discharge area. The runoff condition of the groundwater subsystem in the western region is better than that in the eastern region,and the groundwater circulation speed is faster. Thus,the contribution of water–rock reaction to the chemical components of unconfined groundwater is much lower than that in the eastern region and little dissolution of halite occurs.Consequently,the water quality of the groundwater subsystem in the western region is better than that in the eastern region. The results of this study provide a scientific basis for the optimal allocation and sustainable development of the groundwater resources in arid and semiarid basins of Northwest China.