CO2 heat pump system capable of heating and refrigerating through single-stage and double-stage switching

The invention discloses a CO2 heat pump system capable of conducting heating and refrigerating through single-stage and double-stage switching, and relates to the technical field of CO2 heat pumps, a heat pump mainly comprises a high-pressure compressor, a low-pressure compressor, a four-way reversing valve, a water side gas cooler, a heat regenerator, a first throttling valve, a flash evaporator, a second throttling valve, an air side evaporator and some pipelines and valves. Two single-stage heating cycles and one double-stage heating cycle of the heat pump system are achieved by adjusting opening and closing of the valves, one single-stage refrigeration cycle is achieved through the four-way reversing valve, it is guaranteed that the heat pump system can conduct single-stage heating and double-stage heating according to the environment temperature in winter, meanwhile, refrigeration is conducted in summer, and according to the requirements of users, the heat pump system can be used for heat pump heating. A