Peen forming is an important process for the manufacturing of integral wing skins. In order to design the initial blank shape from the three-dimensional computer model for this process, a computer-aided method is presented. Based on the assumption of small curvatures produced by peen forming, this method deals with quadrilateral mesh, hypothesised in-plane deformation, and minimising the area error of mapping. The algorithm is applied to several examples in order to confirm its validity.