Abstarct: Aq Qalla-Gomishan with an area of 1554/31 km2 is located in Golestan province and east of the Caspian Sea. In order to study hydrogeological and hydrogeochemical, piezometric water level information in the aquifer, as well as 25 water samples taken from wells in the plain and one water sample from the sea have been used. Iso-potential and flow direction maps show that the main aquifer is fed from the east and southeast of Alborz mountain range and a small part of the northern plains and the general direction of groundwater flow is from the east and southeast. It is towards the southwest and the Caspian Sea, which is in the same direction as the surface currents of the Gorgan River. The maximum groundwater gradient is observed in the eastern and southeastern parts. According to the plain unit hydrograph, the general trend of groundwater aquifer level is the same and shows very small changes of about 14 cm/year. The map also shows that the lowest drop is related to the feeding area and the entrance of the plain and the highest drop is related to the discharge and exit area of the plain due to low feeding and harvesting from wells. According to the maps of electrical conductivity changes in three different years, the amount of electrical conductivity increases in the direction of groundwater flow from the supply area to the discharge area. So that the minimum electrical conductivity of 800 μs/cm was observed in the easternmost part and the maximum electrical conductivity of 4300 μs/cm was observed in the westernmost part. Hydrogeochemical and isotopic studies of the study area indicate that the source of groundwater is the atmospheric waters of the present age, mainly of Mediterranean origin, and the source of salinity is the infiltration of saline seawater or evaporation dissolution.