Abstract: Traditional direct expansion solar-assisted heat pump system has poor adaptability in low temperature environment,which affects its use in cold areas. By adopting vapor- injection（VI）technology,it can effectively improve its heating capacity under low temperature conditions. Taking the proposed vapor-injection heat pump system using PVT collector/evaporator as the research object,the effects of environmental conditions,solar irradiance and injected steam mass flow rate on the performance of the heat pump system are simulated and verified by means of model establishment,numerical simulation and experimental research. The simulation results show that the system COP could reach 4.3 which is 63.6% higher than that of the ASHP system with VI cycle when the ambient temperature is - 10 ℃ and the solar radiation intensity is 500 W/m~2. Compared with other three heating systems with Levelized Cost of Heat（ LCOH ）as an indicator,the proposed system economy also has certain advantages,which provides the possibility for the application of steam jet heat pump system in cold area.