Non-cylinder pin hole whose axial section is trumpt and cross section is ellipse, which is very complicated, is difficult to machine with a general NC boring machine. In this paper a new type of high frequency microfeed boring mechanism is designed. Basic idea of this mechanism is asymmetry of stiffness, which will make displacement different of both sides under same stress conditions. It will lead tool rod to oscillate and realize radial displacement. Structure design is completed in SolidWorks and static stiffness, dynamic stiffness, fatigue strength and harmonic response are analyzed based on ANSYS Workbench to assess the design and make optimization improvement. Finally, a processing experiment is done with optimized result, the result shows that optimized mechanism can process non-cylinder pin hole.