Abstract: Carnot battery is a new type of large-scale energy storage technology, which has the advantages of long storage time, low cost and not limited by geographical conditions. In this paper, a Carnot battery system based on transcritical CO2 cycle was established, and the influence of design parameters on the system performance was analyzed by using round-trip efficiency χ, total equipment investment cost Ctot and LCOS as evaluation indexes. The results show that the inlet and outlet pressure of the compressor(pump) has a significant impact on the system performance. Reducing the inlet pressure of the compressor or increasing the outlet pressure of the compressor can significantly improve the round-trip efficiency of the system and reduce the LCOS. The heat storage temperature has a special effect on the round-trip efficiency of the system. With the increase of the heat storage temperature, the round-trip efficiency χ decreases first and then increases. Based on the Carnot cell mathematical model and non-dominated sorting genetic algorithm (NSGA-Ⅱ), multi-objective optimization of the system was carried out, and the multi-criteria decision-making method was used to obtain the optimal solution of the system under multiple decision preferences, which provided theoretical guidance for the design and parameter optimization of the Carnot cell system under different scenarios.