The non-linear temperature glide in the supercritical CO2 cooling process makes the heat transfer pinch point of heat exchanger show multiplicity,like size,location distribution and quantity,which makes the thermodynamic performance of the CO2 transcritical cycle more complex and eventually affects the evaluation of the optimal operating state of the system.Based on the second law of thermodynamics and the constraints of heat transfer pinch,a thermodynamic evaluation method of CO2 transcritical heat pump system was proposed according to the degree of temperature matching.The influence mechanism of multi-characteristic change of heat transfer pinch point on temperature matching degree and the effect of temperature matching degree on thermodynamic performance of CO2 transcritical heat pump system were discussed.The relationship between temperature matching degree,COP and exergy efficiency of the system was analyzed.It is considered that the change of temperature matching index value can clearly characterize the change trends of COP and exergy efficiency.That is,the smaller the temperature matching degree is,the closer the temperature distribution of heat transfer fluids on both sides of the heat exchanger is to Lorenz cycle,and the greater the COP and exergy efficiency are.Furthermore,by monitoring the outlet temperature of the CO2 cooler,which has an essential relationship with the temperature matching degree during the heat exchange process,the deviation between actual and optimal working condition can be judged online,which is beneficial to real-time evaluation of the working state of the system.