During the long-term use of lithium battery packs, there is a problem of inconsistent voltages among the series-connected individual bat-teries. To solve this problem, a cascade bidirectional Cuk equalization circuit system based on variable domain fuzzy PID control is pro-posed in this paper. In this system, a cascade bidirectional Cuk equalization circuit is employed to achieve equalization between non-adjacent cells, and the variable domain fuzzy PID algorithm is exploited to enhance the voltage equalization speed. To verify the fea-sibility and superiority of the system, simulation models of the traditional bidirectional Cuk equalization circuit and the cascaded bidirec-tional Cuk equalization circuit were designed in MATLAB/Simulink. The comparison of simulation results under the control of the fuzzy PID algorithm and the variable domain fuzzy PID algorithm reveals that the balancing time of the cascade bidirectional Cuk balancing topology based on the variable domain fuzzy PID algorithm is decreased by 64.29% compared with the traditional bidirectional Cuk bal-ancing topology without a control algorithm. The equalization time of the cascade bidirectional Cuk equalization topology without a con-trol algorithm is reduced by 50.82%. The balancing time of the cascade bidirectional Cuk balancing topology based on the fuzzy PID algorithm is reduced by 14.29%. According to the analysis of the simulation results, it is demonstrated that the cascade bidirectional Cuk equalization circuit system based on fuzzy PID control in the variable theory domain can augment the voltage equalization rate of the bat-tery.