The utility model relates to a prestressed ground anchor device for foundation pit supporting. The prestressed ground anchor device comprises a horizontally-arranged ground anchor lacing bar and a vertically-arranged anchor pile; an anchor pile top hook is arranged at the upper end of the anchor pile; a horizontally-arranged screw rod is welded at the end part of the ground anchor lacing bar, and is sleeved with a steel pipe; the outer wall of the steel pipe is welded with the anchor pile top hook; a nut is mounted at the end, close to the anchor pile, of the screw rod, and in the position propped against the steel pipe. According to the prestressed ground anchor device, by fastening the nut propped against the steel pipe welded with the anchor pile top hook, the screw rod and the ground anchor lacing bar move to the side towards the anchor pile, so that the prestress is applied to the ground anchor lacing bar to enable the ground anchor lacing bar to be in a tense state at an initial state, and a strengthening role can be played without the displacement of a foundation pit per se; the prestressed ground anchor device is simple in manufacture and strong in economy.