This paper studies a new quasi-two stage compression transcritical CO2 heat pump system with ejector and internal heat exchange. This paper evaluates a dynamic simulation model and analyzes the change factors of COP and compressor power consumption when changing the flow of hot and cold water, intermedium pressure and air cooler inlet temperature. The results show that with the increase of the gas supply pressure, the heating COP of the system also increases, while the heat capacity increases first and then gently. However, when changing the flow of hot and cold water, the system COP increases with the increase of water flow, and the system COP of 0.5 m3/h increases by 6% compared with 0.2 m3/h.