Experiment of a ground source heat pump system in cold area is studied in this paper. The results indicate that when the operation time increases to 100 hours, COPHP (COP of the heat pump) and COPSYS (COP of the system) decrease from 3.54 and 2.63 to 2.53 and 1.92, respectively. The average values of COPHP and COPSYS are 3.1 and 2.3, respectively. COPHP and COPSYS with 2 compressors at work are 11% and 12.2% higher than COPHP and COPSYS with 4 compressors at work, respectively. The average COPSYS with inverters is 6.42% higher than the COPSYS without inverters.