Abstract: In order to study the performance characteristics of transcritical compressed carbon dioxide energy storage (TC-CCES) system and supercritical compressed carbon dioxide energy storage (SC-CCES) system with the same stages, a compressed carbon dioxide energy storage (CCES) system model based on Brayton cycle was established by Matlab software, the thermodynamic performance and exergy destruction distribution of the system were analyzed, and sensitivity analysis was carried out. Results show that under the design conditions, the cycle efficiency,exergy efficiency and energy storage density of SC-CCES system are 66.78%, 58.43% and 255.63 kW·h/m³ respectively, and those of TC-CCES system are 61.21%, 54.30% and 545.69 kW·h/m³ respectively. Exergy destruction analysis shows that improvement of the heat exchanger performance effectively improves the exergy efficiency of both systems. Increasing the energy storage pressure and energy release pressure and making the ambient temperature close to the critical temperature of CO₂, the cycle efficiency and exergy destruction of both systems will increase, while decreasing the water temperature of interstage cooler can improve the performance of TC-CCES system, but it can't have much effect on SC-CCES system. Under the conditions of two-stage of compression and two-stage of expansion, SC-CCES system has better cycle efficiency and exergy efficiency, while the energy storage density of TC-CCES system is about twice that of SC-CCES system.