Abstract: In the modern power system, the excitation system is an important composition part for the generator set.The failure of the excitation system will threaten the safe and stable operation of the entire generator set.According to typical accident cases of excitation system in recent years, it carried out analysis and corrective measures form the aspects of low-frequency overexcitation fault caused by decoupling logic dead zone, signal test acquisition circuit fault, power unit circuit fault and automatic voltage regulator（AVR） power supply fault and so on.It provides an effective way to solve the excitation system accidents, and reference for accident diagnosis technology development of domestic excitation system.