Abstract: The frequent make-and-breaks of the switches in the Buck-Boost equilibrium circuit could reduce the equalization efficiency; on this basis, the traditional Buck-Boost circuit is improved and a quasi-resonant circuit that can realize the zero-voltage conduction of the switch tube is designed, which is conducive to reduce the switching loss and improve the efficiency of equalization circuit. Aiming to reduce the number of switch make-and-breaks and shorten the equalization time, the equilibrium strategy from the global optimization perspective is adopted, the voltage and SOC are selected as the target balancing variables in sections, and the adaptive grouping equilibrium strategies for inter-monomers, inter-cells and inter-modules are proposed. Taking the battery pack with 8 batteries connected in series as an example, an equilibrium experiment is conducted for quiescence, charging, discharging and floating charge. The results show that the equilibrium circuit and the equilibrium strategies proposed in this paper can significantly improve the equilibrium efficiency and speed compared to the traditional scheme, which can help improve the overall performance and prolong the service life of the battery pack.