The conventional line heating method has been applied for the manufacture of various curved blocks used for hull structures in the ship-building industry. However, it has low economical efficiency and productivity because most of its processes are based entirely on the skillful experience of experts. In this study, a flexible forming process is proposed and utilized to substitute for the conventional manual process. In the proposed process, numbers of punches which have round shapes on the contact tip are adopted to configure an equivalent forming surface according to the arbitrarily curved objective surface. A simple punch height determination algorithm that considers the discrete surface and its spatial planar equations is applied to determine the discrete forming surface composed of the adjusted punches. Punch height data are transferred to a numerical simulation model using ANSYS parametric design language, and finite element analysis is conducted to check the formability of the process. Further, experimental investigations are carried out to verify the feasibility of the process using a flexible forming apparatus. Consequently, it is confirmed that a double-curved thick plate could be obtained by the flexible forming process.