The invention discloses a damping vibration-reduction device for long slings of a suspension bridge. The damping vibration-reduction device comprises a supporting frame, and further comprises a rigidconnecting piece and a displacement transmission rod; the rigid connecting piece is used for fixed connecting of the two slings, a rigid hinging piece is arranged in the middle of the rigid connectingpiece, the top of the displacement transmission rod is hinged to the rigid hinging piece, a supporting piece is hinged to the middle of the displacement transmission rod, and a damper is arranged atthe bottom of the displacement transmission rod; and the supporting piece is fixedly connected with the supporting frame, and the other end of the damper is bolt connection with the a sling fixing plate. According to the damping vibration-reduction device, vibration of the slings are magnified to the bottom of the displacement transmission rod through the supporting frame and the displacement transmission rod, thus the damper fully exerts the vibration-reduction effect, vibration in all directions of the slings can be effectively controlled, the vibration-reduction effect is good, the different slings can be mutually fixed through the rigid connecting piece, and the good vibration-reduction effect and stability can be obtained.