The invention provides an ultra-high-voltage GIS rapid transient overvoltage suppression system. The system comprises a metal tank, the inner part of the metal tank is provided with an isolation gap and unit modules connected with the isolation gap, the unit modules comprise resistors, capacitors, and metal bolts, and the resistors are connected with the capacitors via the metal bolts. According to the system, the inner part of the metal tank is provided with the isolation gap and the unit modules, when rapid transient overvoltage of GIS equipment does not occur, capacitive reactance of the isolation gap is high, a transient overvoltage suppression device can be regarded as an open circuit, and normal operation of the GIS is guaranteed; when rapid transient overvoltage of the GIS equipment occurs, the equivalent frequency of the transient overvoltage is high, the capacitive reactance of the isolation gap is low, the device can be regarded as a large load, and energy of rapid transient overvoltage in the GIS is consumed via the resistors so that the amplitude of the transient overvoltage is obviously reduced, and the technical problem of poor suppression effect of rapid transient overvoltage in the GIS in the prior art can be solved.