The invention discloses a suspension rod tensioning device and a construction method thereof, relating to the field of bridge construction equipment. The suspension rod tensioning device comprises a top seat and a tensioning rod, wherein the top seat comprises an upper base plate and a lower base plate which are fixedly arranged, and an accommodation space is formed between the upper base plate and the lower base plate; the upper base plate is provided with a tensioning hole, and the lower base plate is provided with a notch for being matched with a connecting base of a suspension rod; the tensioning rod passes through the tensioning hole and extends into the accommodation space, and the bottom structure of the tensioning rod is adaptive to be connected with the top of the connecting base of the suspension rod; the suspension rod tensioning device also comprises a force application device mounted on the top seat; and the force application device is used for applying an axial force far away from the direction of the suspension rod to the tensioning rod so as to tension the suspension rod. The suspension rod tensioning device disclosed by the invention is simple in structure, reduces the investment of special equipment, greatly saves the cost, and is capable of tensioning the suspension rod in a narrow space.