When shunt capacitor banks carry out reactive power compensation, due to the improper way of opening up and closing circuit breaker switch, it may cause ferromagnetic resonance between shunt capacitor banks and transformer core coil. Through the phenomenon of the system overvoltage when circuit breaker switch closes over the same period, this paper analyzes volt-ampere characteristic of shunt capacitor bank and transformer core coil, it elaborates the mechanism and characteristics of ferromagnetic resonance when ferromagnetic resonance is occurred, and it presents specific measures that it can effectively suppressed the occurrence of ferromagnetic resonance. Simulation results verify that the theoretical analysis and suppression method is correct.