The present invention provides a shell plating developing method leading to reduction of the amount of machining and improvement of the efficiency in manufacturing the shell plating. In the shell plating developing method according to the invention, a shell plating lattice system is constituted, and the directions in which the curvature of a shell plating P at each lattice point of the shell plating lattice system is maximum and minimum are determined (s102). Also, lines extending in the directions in which the absolute value of the curvature is large and small are determined as a first connection line L.sub.1 and a second connection line L.sub.2 (s104). The first connection line L.sub.1 is developed as a straight line on a flat plate P'' while the length of the first connection line L.sub.1 is maintained. And the second connection line L.sub.2 is developed as a line perpendicular to the straight line on a flat plate P'' in such a way that the integrated value of the amount of machining corresponding to the extension ratio or the shrinkage ratio of the second connection line L.sub.2 is minimum.