Abstract: Eighty water samples were collected from different geothermal fields in Beijing and the following five kinds of characteristics of deuterium excess parameters were analyzed: (1) The average d value of geothermal water is 5.40, the average d value of cold groundwater is 6.04, which is bigger than that of the geothermal water, so the oxygen isotope exchange caused by water-rock interaction is easier in geothermal water than in cold groundwater.(2) The oxygen isotope has remarkable isotope exchange process, and the d value increases with the age of the geothermal groundwater. When the age of the water is (12.76±0.13) ka, the d value is 11.2; when the age of the water is (38.96 ± 0.63) ka, the d value is 14.6. (3) The d value decreases with the depth of the geothermal groundwater in the same area; when the depth is 3221 m, the d value is 3.03; when the depth is 125.13 m, the d value is 5.72.(4) The d value decreases from the recharge area to the discharge area. The average d value is 7.31 in northern recharge area, 5.68 in Beijing depression, and -9.20 at the southern edge of Beijing plain. The velocity of flow decreases with the difference dvalues.(5) The d value increases with the redox potential when it is smaller than 200 mV. When the redox potential is -326 mV, the d value is -9.20; when the redox potential is 158 mV, the d value is 7.48. The d value decreases with the redox potential when it is bigger than 200 mV.