This paper introduces the practical energy performance of medium-depth geothermal heat pump systems (MD-GHPs), which use vertical concentric tube as ground heat exchangers (GHEs) to extract heat from the medium-depth geothermal energy for space heating in buildings. Hereby the medium-depth geothermal energy refers to heat embodied in rocks nearly 2–3 km underground with temperature around 70–90°C. The operation performance and energy efficiency of MD-GHPs is tested in five residential buildings in Xi'an, North China. According to the short-term and annual field test results, the energy performance of MD-GHPs as well as the heat transfer performance of GHEs are introduced and analyzed. Results show that the average temperature of the outlet water from the ground can reach 33.0 °C, promoting the performance of whole systems greatly, with the COP (Coefficient of Performance) of the heat pump reaching 5.43 and the COP_hs of heat source reaching 4.58. Therefore, the energy saving rate (ESR) of the MD-GHPs can reach 41.0%, 29.3% and 47.5% compared with air source heat pump systems (ASHPs), conventional ground source heat pump systems (SD-GHPs) and gas boilers.