Abstract: The defect of internal fold of the hot-rolled seamless steel pipe has been so far one of the major elements which negatively influences the first qualification rate and yield target of steel pipes. The said defect mainly occurs in the piercing process,and the main causes for it are related to both the quality of the continuously-cast billet (the internal cause) and the reasonability of the piercing schedule (the external cause). The analysis focuses on the relationship between the rolling process schedule and the said defect. Accordingly relevant preventative actions are proposed.