Die shape plays a key role in extrusion process through widely affects on the extrusion pressure and product quality. Therefore, prediction of the optimal die shape is the main objective for an effective extrusion process. In this study, the notion of Equi-Potential Lines (EPLs) was applied to 3D-die designing in extrusion process for the first time. To implement the analogy in the extrusion, the initial and final shapes were considered and two different potentials were assigned to them, and then EPLs were drawn between two shapes that show the minimum work path between the entry and exit cross sections. The drawn EPLs were connected to build up a 3D-die. The effectiveness of the proposed method was examined experimentally, by comparing the results between the designed die and the linear die (with the linear curve for the deformation zone). It was found that there was acceptable reduction in extrusion pressure for the designed die.