The invention belongs to the peen forming technology, which relates to a peen forming method for a ribbed structure. The method comprises the following steps: first, the section of the ribbed structure is calculated by the areal coordinate formula used for calculating section graphic in material mechanics for determining the position of a neutral axis of the ribbed structure section; and then thepeen area is determined by the exterior of the ribbed structure. When the required bending deformation amount of the ribbed structure is relatively large, the ribbed structure can be put on a pre-stressed fixture, elastic pre-bending force is applied to the ribbed structure along the direction of the rib, and then peen forming can be conducted. The method determines the tensile deformation area to be the peen area through the rib bending neutral axis and shields the non-peen area at the same time, so as to realize the peen bending forming of the integral ribbed structure; therefore, in the bending forming process of the ribbed structure, no torsion, flexure, sectional distortion, and the like phenomena happen. The method of the invention is also applicable to the peen bending forming of the integral structures with I-shaped or inversed-T-shaped rib section shapes.