The invention relates to a superfast transient overvoltage generating device. The device comprises a barrel body and electrodes used for the connection of power, the inside of the barrel body from the root to the end is in sequence provided with a discharge gap module, a first interface for the connection of inhibition equipment, and a second interface and a bus, through the supply of voltage to the discharge gap module the electricity discharge gap is broken down, and superfast transient overvoltage is generated, to simulate the process of generating superfast transient overvoltage by disconnecting the switch. The device does not require the provision of an engineering site, the superfast transient overvoltage generation circuit can be built in a test station or a factory, the circuit can simulate the voltage waveform of superfast transient overvoltage under different situations, and is used for achieving the testing of the inhibition performance of the inhibit equipment in a laboratory environment.