The invention discloses a cold reinforcement structure for the external deformation fatigue of a steel bridge deck. Flange plates are arranged on the upper and lower ends of a web plate, stiffening ribs are arranged on the side surfaces of the web plate to form I steel beams, at the gap of the web plate among the stiffening ribs and the flange plates, one branch of angle steel is connected to the stiffening ribs, and the other branch of the angle steel is connected with the flange plates or the web plate by connecting piece, the connecting pieces are structural adhesive, bolts or screws, the structural adhesive or bolts is or are adopted to connect one branch of the angle steel with the stiffening ribs, and the structural adhesive, the bolts or the screws is or are adopted to connect the other branch of the angle steel with the flange plates; the structural adhesive or bolts is or are adopted to connect one branch of the angle steel with the stiffening ribs and connect the other branch with the web plate. With the cold reinforcement structure, the rigidity of the gap of the web plate among the vertical stiffening ribs and the flange plates of a steel bridge is improved, the deck external deformation at the gap of the web plate is reduced, so that the purpose of reinforcing the deformation fatigue details at the exterior of the gap surface of the web plate is realized. Meanwhile, the cold reinforcement method is adopted, the adverse effects such as welding residual stress are not introduced, and the cold reinforcement structure has the advantages that the operation is simple, the cost is low, and the performance is good.