The high efficiency water source heat pump unit suitable for utilizing the low water temperature of river, lake and sea has two stages of water source heat pump. The two stages of water source heat pump, each of which comprises evaporator, refrigerating compressor, condenser and expansion valve, are connected by means of the circulating pipeline with circulating water pump and pressure stabilizing water replenishing tank. The first stage of the water source heat pump has its evaporating temperature and condensing temperature determined based on the water source temperature, so as to provide the second stage with proper input water source temperature and to make the water source heat pump unit operate in high efficiency under the low water source temperature condition of lower than 2deg.C. |