Abstract: By analyzing the δ¹⁸O and δD isotopic data of Xi'an and Xianyang,this paper studies the features of the deuterium excess(dexcess) parameter in thermal groundwater and the effect of the extent of water-rock exchange on d-excess value distribution,concluding that water-rock exchange of low thermal groundwater in Xi'an and Xianyang is not apparent,while the deep is quite apparent and there is oxygen draft.Deuterium exchange of some samples in Xianyang is also apparent.The more closed the aquifer is,the more reductive the geological environment is.The more intense the water-rock exchange is,the smaller the d-excess is.In addition,as the oxygen draft grows further away from the local mean water line,the d-excess gets smaller,the depth gets deeper,the residence time gets longer,the total dissolute solid gets bigger,the temperature of thermal groundwater gets higher.