The present invention discloses an embedded steel bar straightening device and an application method thereof. The device comprises pedestals fixed at two sides of a structure embedded steel bar position via expansion bolts; sliding supports slidingly sleeving the pedestals, wherein positions of the sliding supports are fixed by fixing bolts; a plurality of supporting bars, wherein the bottoms of the supporting bars are disposed on the sliding supports, and the tops of the supporting bars are connected to form a supporting bar connection point; and a hydraulic bar, wherein the top of the hydraulic bar is connected with a power line and the supporting bar connection point, and the bottom of the hydraulic bar is hinged to an annular sleeve via a rotating shaft pin. According to the embedded steel bar straightening device and the application method thereof, the problem that embedded steel bar straightening is difficult is solved, the steel bar straightening effect is good, working efficiency is high, and labor is saved; manpower is replaced by electric power, which brings greater economic benefits; and the device is simple and easy to operate, safe and easy to maintain, and easy and simple to handle, and can be widely promoted and used.