Abstarct: In arid and semi-arid regions, due to low rainfall and excessive withdrawal from groundwater sources, followed by the advancement of the saline water front, the available fresh water resources have decreased. With the disruption of the hydrological balance of groundwater, the increasing salinity, and recent droughts, the issue of water crisis in the Davarzan plain has emerged. The Davarzan plain, located in the west of Khorasan Razavi province, covers an area of 19,898 square kilometers. To investigate the hydrogeochemical evolution of groundwater resources, 24 water samples were collected from existing exploitation wells in the Davarzan plain, and hydrochemical and isotopic analyses were performed. According to the potentiometric map and flow direction in the plain, the aquifer is mainly recharged from the ophiolites in the northern parts of the plain and discharges towards the southern and southwestern parts. The variations in electrical conductivity are almost in line with the groundwater flow direction. The electrical conductivity ranges from 430 µS/cm in the northern parts to 4400 µS/cm in the southern and western parts of the plain. The increase in salinity in the southern part could be due to the concentration of withdrawal wells near the salt flats in the southern part of the plain, causing partial salinity infiltration into these areas. Given the shallower wells and groundwater in this southern part, the likelihood of saline water infiltration from below towards the wells also exists. However, due to the increase in salinity and its impact on agricultural products, the amount of withdrawal has been forcibly reduced, leading to a reduction in the rate of saline water infiltration and consequently a slight decrease in the salinity of the plain. Therefore, reducing water withdrawal has had an effect on reducing salinity in the region. Considering the lack of a significant increase in salinity in the plain, it is likely that fresh water has flowed towards the saline water, causing the phenomenon of freshening. The pH values in the groundwater resources of the region range from 8.12 to 9.41. The water type in the fresh samples is sodium bicarbonate, and in the saline waters, it is sodium chloride. All water samples in the region are supersaturated with respect to calcite and dolomite and undersaturated with respect to gypsum and halite minerals. baxsed on hydrochemical analysis and statistical analysis, the origin of the ions in this area could be influenced by the dissolution of salts, as well as the dissolution or precipitation of carbonates and possibly significant weathering of pyrite. Cation exchange phenomena could also occur as a secondary process given the changes in ion concentrations in this plain. According to isotopic results, the primary source of Davarzan plain waters is atmospheric, and over time and distance from the recharge area, the isotopic values, especially oxygen-18, have changed. The isotopic change behavior does not match the salinity of the plain. Secondary processes such as saline water infiltration or carbonate precipitation may have somewhat influenced the isotopic changes in the plain.