The invention discloses an overvoltage relief device of an insulator, which is arranged on the insulator which is provided with a metal cap, a line pressing device, a metal base and a ceramic body. The overvoltage relief device comprises a protective cover and an overvoltage relief electrode, wherein the protective cover is arranged on the metal cap, and the overvoltage relief electrode is arranged on the metal base; and an overvoltage relief groove is arranged on one surface of the protective cover which is in contact with the metal base. The technical scheme has the following beneficial effects that: as the overvoltage relief groove is arranged on one surface of the protective cover which is in contact with the metal base, the metal cap can be used as a part of the overvoltage relief electrode, thereby the overvoltage relief electrode arranged on the metal cap is omitted so that the production cost, the management cost, the distribution cost and the working hour of installation and maintenance are greatly reduced.