The invention discloses an improved lightning protection post insulator, which comprises an insulator main body, and an upper cap and a lower flange which are respectively arranged at the two ends of the insulator main body, wherein an insulated cable is installed at the top of the upper cap, the improved lightning protection post insulator further comprises a jointing clamp, an insulating cover and an insulating sheath, the jointing clamp is assembled at the top of the upper cap, and the insulated cable is pressed between the jointing clamp and the upper cap and is covered by the insulating cover from the top of the insulated cable to the upper cap; and the insulating sheath wraps the opening of the upper end of the lower flange. The integral product processes can be reduced, so the labor intensity is decreased, and mistakes and omissions are eradicated; the electric discharge between the upper cap and an electric discharge ring is avoided, so the electrical connection performance is improved; the eddy-current loss is reduced, so the power quality is improved; and the distance between an electric discharge point and a porcelain insulator is increased, so the damage of the lightning current to the porcelain insulator is reduced.