Under transformer no-load or light load operation, shunt capacitor banks and transformer core coil may cause the ferromagnetic resonance because of line breaks or circuit breaker asynchronous closing and then overvoltage is generated. Taking single-phase disconnection fault occurred in the power system for example, this paper derives resonance condition expression between the gird voltage and shunt capacitor capacitance. When ferromagnetic resonance is occurred, the mechanism and characteristics of ferromagnetic resonance generated by shunt capacitors and transformers are elaborated through analyzing the volt-ampere characteristic between shunt capacitor bank and transformer core coil, and specific measures that can effectively suppress the occurrence of ferromagnetic resonance are presented. Simulation results verify that the theoretical analysis and suppression method is correct.