Abstract: Combined with the emergency shutdown of protection caused by thermal signal in a power plant of Huadian Group, through fault analysis and inspection, it is found that the accident was caused by the action of “mechanical and hydraulic overspeed of 150%Ne” of No.2 unit protection PLC. The problem is deeply analyzed from three aspects of management factors, technical factors and equipment factors, and then the preventive measures are implemented to ensure the safe and reliable operation of equipment.