Abstract: Investigated are the specific causes for occurrence of tail-end fins of the pierced shell， involving such aspects as metal plastic deformation，billet temperature and roll rotation speed，etc.Accordingly，preventative actions are proposed，and advantages and disadvantages of the actions are compared with each other.As a result，it is concluded that the occurrence of the said fins can be properly prevented by means of billet tail-end centering，restraining temperature over rise of the billet’s tail-end internal metal，and decreasing the shear stress thereof.Nevertheless linear control of the piercing roll rotation speed is the best way to prevent occurrence of the fins during the piercing operation.