The invention discloses a reinforcing method of a simply-supported plate beam bridge for heavy-cargo transportation and belongs to the field of construction methods. According to the method, a high-strength tensile material is arranged at the bottom of the bridge, and the rigidity of the bridge is improved; and hinge joints are filled with high-strength adhesive materials, and the integrity of the bridge is improved. The invention further provides a reinforcing method for the state that a support is not suitable for being erected below the simply-supported plate beam bridge for construction. Lifting equipment is erected at the two ends of a beam plate hinge joint. Lifting ropes are used for lifting an H-shaped steel beam in plate through the hinge joint. A containing cavity is formed among the upper flange of the H-shaped steel beam, a strip-shaped blocking sheet and the beam plate bottom face with the hinge joint. The high-strength adhesive material is poured into the beam plate hinge joint, and the containing cavity and the hinge joint are filled with the high-strength adhesive material. According to the method, the high-strength tensile material is arranged at the bottom of the bridge, so that the rigidity of the bridge is improved; and the hinge joints are filled with the high-strength adhesive materials, the integrity of the bridge is improved, and finally the simply-supported plate beam bridge has the capacity of heavy-cargo transportation.