Since the micro-diameter lettering knife open half long, low rigidity of the cutter body, plus overhang large, easy to produce vibration when machining, affect the surface quality and tool life. Theoretical analysis shows that: the tool deformation amount increases with the overhang extending the amount becomes large, as the tool overhang reach 18 mm, the amount of deformation increased rapidly; by the tool to improve the modal analysis tool structure, decreases the opening half length, thereby increasing the rigidity of the tool, the tool helps reduce vibration.