The invention relates to an overvoltage warning device. According to the structure of the overvoltage warning device, the output end of a voltage transformer is connected with the input end of a dual-voltage comparator; the output end of the dual-voltage comparator is connected with a microprocessor and a timer; the microprocessor is connected with a power source and an alarm circuit; the alarm circuit is connected with an indicating lamp; the dual-voltage comparator is provided with a dual-operational amplifier; and the dual-operational amplifier is connected with a negative temperature coefficient voltage-regulator diode, a single comparison reference power source circuit and a resistor. The overvoltage warning device of the invention can perform warning timely when overvoltage occurs, so as to ensure the safety of a circuit. The overvoltage warning device of the invention has the advantages of convenient installation and use, high reliability and high practicability, and is suitable for being popularized and applied.