Abstract: Analyzed are the defective inner surface spiral mark as developed with the hi-Cr alloy steel pierced shell, and the reasons for such a defect.Accordingly countermeasures are put forward.It is identified via the analysis that the main reasons for occurrence of the said spiral mark is in-process consistent wearing of the Mo plug, and the rather short rounding-sections of the plug end part.In this case the wear-resistance of the plug will be increased by means of optimizing the plug profile, e.g., shortening the length of the piercing taper, and reducing the taper degree itself.As a result, the inner surface spiral mark will be reduced so as to improve the pierced shell quality, and increase the service span of the Mo plug, and in turn have the productivity enhanced.