The invention discloses a warning device for road and bridge construction. The warning device for road and bridge construction comprises a bottom plate, a movable plate, a first motor, a bidirectionalscrew rod, an inner threaded sleeve, a connecting rod, a mounting plate, a second motor, a first rotating shaft, a second rotating shaft, L-shaped rods, a warning board, a rotating sleeve, a connection bar, a movable rod top end and a warning lamp, wherein the first motor, the bidirectional screw rod, the inner threaded sleeve and the connecting rod are arranged so that the height of the whole warning device can be adjusted, and the adaptability is high; the second motor, the first rotating shaft, the second rotating shaft, the L-shaped rods, the connection bar and the movable rod are arranged, the second motor drives the first rotating shaft to rotate, the first rotating shaft drives the L-shaped rod at the top end of the first rotating shaft to rotate, and meanwhile, under the matchingof the second rotating shaft and the L-shaped rod at the top end of the second rotating shaft, the warning board is driven to continuously move, people are reminded to pay attention to the warning board, and the warning effect is good; and in the rotating process of the L-shaped rods, the movable rod is driven to move left and right through the rotating sleeve and the connection bar, and the movable rod drives the warning lamp to move left and right, so that the warning effect is further enhanced.