Spin forming is a new manufacturing process for cup shaped thin wall inner gear. This technique can be used for forming two types of inner gears. One is internal spline, and the other is inner gear.Analysis of gear parameters on impact of cup shaped thin wall inner gear spin forming,and the spinning process for the two types of inner gears were discussed based on the experimental investigation. It shows that the larger number of gear tooth would result in reducing the inside diameter of the part; the increase of tooth thickness is favorable for the metal flowing in radial direction and less favorable for the metal flowing in tangential direction; radial reduction and feed ratio have a significant effect both on straight line inner gear and involute inner gear.