Abstract: To address capacity degradation and reduced cycle life in series-connected lithium-ion battery packs caused by cell inconsistency, and to overcome the slow equalization speed of traditional Buck-Boost circuits in long battery strings, this paper proposes an active equalization system based on an improved Buck-Boost circuit. By constructing a multi-level equalization topology, the system enables parallel energy transfer both within and between battery modules, effectively resolving the slow adjacent-cell balancing limitation. Using State of Charge (SOC) as the primary equalization criterion supplemented by voltage thresholds, an intelligent active-passive coordinated balancing strategy is implemented. A simulation model for a 6-cell system was developed on Simulink and validated under three conditions: static, charging, and discharging. Results demonstrate that compared to conventional Buck-Boost circuits, the proposed topology achieves: more than 40% average increase in equalization speed across all states87.5% maximum improvement (notably enhanced with larger initial SOC differences) This conclusively verifies the system’s superiority in accelerating equalization and optimizing overall pack performance.