<p>The liner of a CNG high-pressure vessel is manufactured by a D.D.I. (deep drawing and ironing) process for the cylinder part, which is a continuous process that includes a drawing process to reduce the diameter of the liner and a subsequent ironing process to reduce the thickness of the liner. In this study, the new process planning was designed to improve productivity in the manufacturing of a CNG pressure vessel (Type II) liner using Forge Nxt 3.2 software. While the conventional D.D.I. process is performed in three stages by separating the drawing and ironing processes, this study reduced the number of stages by integrating process and reflecting design rules in the actual field. In the first stage, a tractrix die with the maximum draw ratio that prevents fracture was designed and integrated with two ironing dies designed according to field design rules. Therefore, the integrated die capable of continuously performing deep drawing and two ironing processes was developed, while evaluating forming defects and punch loads using finite element analysis (FEA). Based on these results, the conditions were determined to complete forming process in the second stage. Consequently, the total number of forming stages was reduced from three to two, thus improving productivity and reducing manufacturing cost.</p>