When batteries are used in group, the states of charge (SOCs) and voltages are inconsistent between single batteries due to different manufacturing processes and working environments. In order to solve this problem, a battery equalization system based on coupled inductor double-layer Cuk chopper circuit is proposed, in which the coupled inductor is used instead of the uncoupled inductor. Compared with the traditional Cuk chopper circuit, it reduces the number of components, lowers the loss and improves the equalization efficiency. At the same time, the equalization system uses the N-channel MOSFET, which is controlled by a pair of complementary signals in synchronous trigger pulse PWM. Through the circuit theoretical analysis, a complete equalization circuit is designed. Finally, simulation is carried out in MATLAB/ Simulink. The results verify the efficiency of the equalization system.