The invention relates to a method and device for testing a very fast transient overvoltage (VFTO) suppression device. A specific value of the first peak value V1 of a signal generated after VFTO suppression to the first peak value U1 of a signal generated before VFTO suppression is compared with a set first allowable value, and a specific value of the second peak value V2 to the first peak value V1 of a signal generated after the VFTO is suppressed by the suppression device is compared with a second allowable value, so as to test the suppression effect of the suppression device for a VFTO signal generating circuit. The method is simple in principle, high in test reliability, and good in suppression effect, can accurately obtain the suppression performance of the suppression device to guide the selection of the better and more economical suppression device, does not need field testing, and can test the VFTO suppression performance just in a test station or manufacturer.