Aiming at the temperature inconsistency of series-connected lithium-ion battery packs, a thermal balance control strategy for lithium-ion battery packs based on bi-directional flyback converters is proposed. This strategy can ensure that the system tracks the reference value of the output power of the system, and uses the surface temperature of the lithium-ion battery as the balance criterion. By adjusting the balance current of the bi-directional flyback converter circuit, the temperature balance in the series-connected lithium-ion battery pack can be achieved. It overcomes the battery inconsistency problem caused by the high temperature of batteries, avoids the safety problems of battery pack life degradation or thermal runaway caused by the short-board effect of accelerated aging of some cells, and ensures the stability and safety of the system. A simulation experiment was carried out on the MATLAB/Simulink and COMSOL co-simulation platform to verify the effectiveness of the control strategy.