The change of stress caused by fault activity will break the balance of water-rock reaction of groundwater,which will lead to the change of hydro-chemical type and hydrogen oxygen isotopic composition. In this paper,we analyzed ion chemical composition and hydrogen oxygen isotope of fluid from Hejiazhuang observation well,and studied the geochemical characteristics of the well and the relationship with tectonic activity. Firstly,based on the results of hydrogen and oxygen isotopes and elevation effect,we determined that the main source of well water is atmospheric precipitation,which infiltrates along fracture fissures,increases temperature after deep circulation,and forms hot water through dissolution and filtration. Then with accordance to Shukarev classification,the water type of Hejiazhuang well is classified into Cl-Na.Ca type,which is under the influence of Changli M4.2 earthquake on September 14,2015. We believed that the regional stress change increased the rock fracture in the fracture zone of the borehole,and the deep hot water upwelling,resulting in the change of ion composition and hydrogen oxygen isotope composition of the well water in Hejiazhuang. The results show that the geochemical characteristics of the fluids in Hejiazhuang well can provide geochemical basis for the analysis of the fault structural activities and the earthquake precursor anomalies near the fluid observation well.