The liner of type 3 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 billet and a subsequent ironing process to reduce the thickness of the billet. But the wall thickness of type 3 pressure vessel liners used in vehicles and ships is required to be 5 mm. Excessive wall thickness not only increases the weight of hydrogen vehicles and ships equipped with type 3 high-pressure vessels but also deteriorates their transportation efficiency. But the forming process of the cylinder part of the high-pressure vessel liner (Al6061) has a total of three stages (first deep drawing with blank holder, second redrawing, third redrawing + ironing) through which the wall thickness is manufactured up to 6.8 mm in the actual field. In this study, the maximum drawing ratio and die inflow angle in the first-stage deep drawing process by using the shape factor formula of the tractrix die and combined process (redrawing + ironing) in the third stage were determined in order to manufacture a liner with a wall thickness of 5 mm within the existing three stages, including saving of die costs. Using damage value verified through finite element analysis and experiment and based on the above results, design of the D.D.I. process (three stages) was performed, and its results were verified.