SPF process for titanium semi-annular part had been researched in this article. A direct-reverse SPF process was intended for controlling the thickness of the semi-annular part after forming,and the SPF forming die which is the key for the thickness control had been designed and optimized by numerical simulation method.Verification experiment was preceeded for a TC4 semi-annular part,the results show that the actual thickness distribution of the part can be well predicted by the numerical simulation,the thickness of the part was homogenized by using optimized SPF forming die.This process can not only improve material utilization ratio and efficiency of subsequent processing,but also reduce total manufactuting costs.