The invention relates to an external gap discharge protection structure for a tension rod insulator lightning arrester, and the structure comprises an upper electrode, a resistor piece and a central electrode of a lightning arrester. The housing of the upper electrode is provided with an upper conductor ball seat in an integrated manner, and the interior of a lower opening of the upper conductor ball seat is fixedly provided with an upper conductor ball. The upper conductor ball is connected with the upper electrode through a wire. The housing of the central electrode of the lightning arrester is provided with an L-shaped support in an integrated manner. The top of the L-shaped support is provided with a lower conductor ball seat in an integrated manner, wherein the opening of the lower conductor ball seat is upwards. The interior of the lower conductor ball seat is fixedly provided with a lower conductor ball. The lower conductor ball is connected with the central electrode through a wire. The upper and lower conductor balls are metal conductor balls of the same type. The opening planes of the upper and lower conductor ball seats are parallel each other, and are perpendicular to the connection line of the centers of the upper and lower conductor balls. The structure enables the discharge voltage of a gap to be low in dispersity, guarantees the matching of the lightning arrester with the volt-second characteristic curve of the insulator, reduces the residual voltage, and improves the protection performance.