The novel Carnot battery energy storage system is proposed by coupling the two-stage compression heat pump (HP) with flash evaporation and organic Rankine cycle (ORC) in the current study. The low-temperature waste heat of sinter cooling flue gas in steel industry is used as the system heat source, and the thermodynamic calculation model of novel energy storage system is established. The change laws of system round-trip efficiency, total exergy loss and exergy efficiency under various HP working fluids and key operating parameters are deeply investigated, and the thermodynamic performance of various HP working fluids under the optimal system operating parameters, as well as the distribution of exergy losses in each system component are also presented. The research results indicate that when the HP working fluid is fixed, the lower the HP condensing temperature is, and the higher the ORC evaporation temperature is, the greater the system round-trip efficiency and exergy efficiency are, while the system total exergy loss is smaller. With the rise of flash evaporation temperature, the system round-trip efficiency and exergy efficiency first rise and then reduce, while the system total exergy loss first reduces and then rises. Under the optimal operating conditions, the R1234ze(Z) set as the HP working fluid has the best thermodynamic performance with the system round-trip efficiency of 64.19%, total exergy loss of 1454.3 kW, and exergy efficiency of 34.97%. Among them, the exergy loss generated in HP evaporator is the highest with a relative exergy loss rate of 24.25%, followed by the irreversible loss in ORC evaporator with a relative exergy loss rate of 20.19%, and the smallest is the irreversible loss in ORC working fluid pump with a relative exergy loss rate of only 0.21%.