This article analyzes the origin and the deep circulation process of low- to- medium temperature geothermal fields distributed within the Huangshadong and Conghua thermal fields in Guangdong Province, basic on the analysis of the hydrochemical characteristics and isotope data of the hot water and cold water in the study area. The thermal groundwater is originated from meteoric precipitation. The Huangshadong thermal field has the characteristics of a deeper circulation, longer cycle period, and smaller cycle rate, which allows it to obtain more heat from the surrounding rock. The Conghua thermal fields have the characteristics of short retention time, strong alternation and weak water—rock reaction. Both thermal fields in study area have two reservoirs, the temperature of shallow reservoir in Huangshadong thermal field is about 125℃, with the depth of the thermal cycle is about 2600m; the temperature of deep reservoir is about 180℃, with the depth of the thermal cycle is about 4000m. The temperature of shallow reservoir in Conghua thermal field is about 90℃, with the depth of the thermal cycle is about 1700m; the temperature of deep reservoir is about 150℃, with the depth of the thermal cycle is about 3200m.