This study assessed a variable flow rate control method for a circulation pump based on the geothermal water temperature difference in a geothermal heat pump system. As interest in energy conservation and efficient use is increasing around the world, the development and use of renewable energy is increasing and various related studies are currently underway. Among the renewable energy systems, the interest in geothermal energy system is high because of its efficient year-round operation. Geothermal heat pump system installations have increased in number, but the systems operate inefficiently. Generally in Korea, geothermal heat pump system operates under partial load conditions, but the circulation pump operates at constant speed and supplies a constant flow rate. Therefore, this study examined the operation of the current problems of a geothermal heat pump system. A variable flow rate control method of the circulation pump is proposed to improve the efficiency of the geothermal heat pump system and save energy during the cooling operation. As a result, the total energy consumption was reduced by 57,017 kW compared to the existing flow rate control method and the energy consumption of the circulation pump system was reduced by 35,209 kW.