Dongda is located in the south of Xi'an City, Shaanxi Province. The region is of alluvial-pluvial plain and rich in geothermal resources. For the purpose of further exploration and sustainable use of geothermal resources, researchers should elaborate genetical mechanism of the geothermal field through the application of hydrogeochemical methods and analyzing regional geological conditions. The results obtained by the authors show that the geothermal field belongs to the low-medium temperature geothermal system of convective type. The regional heat flow is 74.5 mW/m2 without special additional heat source. The recharge area is located to the southwest of the geothermal field and geothermal water originates from precipitation of the Qinling Mountain with a recharge elevation of more than 1320 m. The temperature of the deepest reservoir is estimated to be 110℃, with a deep water cycling of 3120 m. The geothermal water age is about 14461 a. A number of different directions of active faults exist in the region. Under the effect of thermal convection, geothermal water flows upward along the faults and is mixed with more cold water. Because of the overlying Quaternary loose deposits, geothermal water is stored in the shallow reservoir, forming the Dongda geothermal field.