The ferromagnetic resonance is a kind of phenomenon that frequently occurs in the floodgate operation. This paper researches, above phenomenon occurred recently in a power transformer station, which has calculated data and equipment parameter obtained from experiment, listed the equivalent circuit, analyzes the mechanism which the over voltage will produce, discovers the true reason which the resonance occurred is the improper match of circuit breaker parameter and the voltage transformer parameter, and proposes the corresponding solution in following aspects such as equipment shaping, operation sequence, two-times preventive method and so on.