Abstract: Described are the key equipments, proc ess parameters and process flow of the new type multiple function piercing-rolling mill for large diameter seamless steel pipes. The important characteristic of the mill is that the two procedures of piercing and rolling, or primary piercing and secondary piercing, can be completed continuously within a limited time on one set of equipment. The mill is especially suitable to be used to produce the seamless steel pipes with large diameter and small batch quantity and the production cost of the large diameter seamless steel pipes with multi sizes and small batch quantity are greatly reduced with the use of the mill, which surely is a new breakthrough in the production technology and process of the large diameter seamless steel pipes.