The invention discloses a prestressed fiber board tensioning device. A groove(s) is/are formed in one end/two ends of the reinforced position of the surface of a beam plank; a fixing steel plate is arranged in the groove; a fiber board is fixed to the reinforced position, one end of the fiber board is fixed to the beam plank/the fixing steel plate, and the other end of the fiber board is fixed to the fixing steel plate; the fiber board and the fixing steel plate are fixed by a first anchoring steel plate and a second anchoring steel plate; the first anchoring steel plate is arranged at the end of the fixing steel plate in the length direction, and the second anchoring steel plate is arranged at the other end of the fixing steel plate in the length direction. According to the invention, the bonding performance of the fiber board and a concrete beam can be obviously improved, a reinforcement material, such as the fiber board, is fully bonded to the reinforced beam plank, the use efficiency of the material is improved, anchorage segments are effectively prevented from tilting, and the reinforcement effect is enhanced.