The utility disclose a outdoor fire hydrant seal structure comprising a valve core, a seal seat, a sealing gasket at lower part of elevated screws, a abrasion-proof cover closely matching with lower part of step-shaped inner ring extended by fire hydrant valve body seat bore central part; the valve core, seal seat and sealing gasket are connected together; the valve core is in clearance fit with fire hydrant valve body seat inner ring; the seal seat and seal gasket are positioned under valve body seat inner ring; the diameters of seal seat and seal gasket are larger than inner diameter of abrasion-proof cover. The outdoor fire hydrant seal structure is mainly subject to self pressure seal of water medium; the more water pressure of water inlet, the better the seal performance; So contact part damage is improved and service life is prolonged. Even if overground portion of fire hydrant is destroyed, the self-locking function of fire hydrant can guarantee good seal for a long time.