A tubular shafts have been considered for weight reduction and high quality in the automobile industry. However, in the case of long and thin tubular shafts, it is very difficult to form an internal spline under a cold extrusion process due to folding and buckling. In this study, multi-stage forming is applied to form precise teeth shape in a long and thin tubular shaft. The effects of die diameter and thickness of the material are investigated and analyzed to determine the number of processes based on a FE simulation. Extrusion experiments have been performed to verify the results obtained in the FE simulation. It is confirmed through these tests that a long spline shaft with high dimensional accuracy and improved mechanical properties is formed.