Owing to the present more stringent exhaust emission regulations, it becomes increasingly significant that the 3D fins on the surface of stainless steel strip used as the metal carrier of a catalytic converter is machined to improve substantially the effectiveness of the converter. Thus in this work, the mechanism of pre-roll ploughing on the surface of stainless steel strip was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. Further, the proper mathematical model was established. Based on the volume of fin ploughed out being equal to the volume of the metal extruded up by the extruding face of the tool, the relation of the fin height, the distance of interval tools and the ploughing depth has been achieved. The distance of the interval of the tools has a great effect on fin height: with the increase of the distance of interval of the tools, the fin height gradually decreases. With the increase of ploughing depth (equal to groove depth), the fin height becomes larger. The theoretical analyses basically accords with experimental results. The conversion rate of a catalytic converter using a fin metal carrier is 12-15% higher than that of a catalytic converter using a smooth metal carrier of identical volume.