The invention relates to the electric power aerial line lightning protection technical field, and discloses an insulator lightning protection device capable of adjusting a discharging gap; the insulator lightning protection device comprises an insulator; the insulator comprises a porcelain body, a core bar, and a steel cap; the steel cap has a connecting lug with a connecting hole; the core bar is provided with a rod electrode; one end of the rod electrode is provided with threads; the core bar is provided with an electrode positioning hole; the rod electrode penetrates the electrode positioning hole and is locked by a nut; a stud is arranged in the steel cap connecting hole; one end of the stud is welded with a connecting rod; the other end of the stud is locked by a nut; a rectangular hole penetrating two sides of the connecting rod is arranged outside the connecting rod; a slide piece is arranged in the rectangular hole; the slide piece outer end bends and extends to form a connecting piece; the connecting piece is provided with a plate electrode; the side face of the connecting rod is provided with a locking bolt used for fixing the slide piece. The insulator lightning protection device can adjust the gap, and is stable in lightning protection effect.