The present invention provides: a tendon anchor system of a long span fire-resistant deck prestressed and anchored on a deck end part, the tendon anchor system applying a bending displacement amount in the upward direction without damaging or breaking a deck plate, and making the arrangement direction of a tendon at the anchoring position thereof be consistent with the prestressing force direction; and a construction method thereof. A tendon anchor system of a long span fire-resistant deck prestressed and anchored on a deck end part, according to an appropriate embodiment aspect of the present invention, relates to a tendon anchor system for controlling, by a tendon, the deflection of a deck plate main body supported and provided on H-shaped steel beams, which face each other, and is characterized in that: the upward position elements of the deck plate includes one pair of steel rod support plates joined by bolts to two upwardly opened concrete-filling valley parts of the deck plate main body so as to face each other, steel rod connection latches respectively joined to the one pair of steel rod support plates, and tendon position steel rods placed by fitting the both ends thereof into the steel rod connection latches, which face each other; tendon anchor units are provided and positioned on the concrete-filling valley parts at the both end part sides of the deck plate main body so as to be supported on end plates; and a tendon is provided such that the both ends thereof are connected to and prestressed by the tendon anchor unit sides and, simultaneously, the remaining section is positioned to come into contact with the bottom surfaces of the tendon position steel rods, which are provided at two places, so as to hinder the ascending force of the tendon.