Abstract: Described here in the paper are several different mandrel rolling & circulating methods. It is regarded that, as the absolute current mainstream of the mandrel mill, the retained-mandrel mill still stays with the problem of rather slow production cycle. To solve the said problem a serial technical optimizations should be taken for the piercing process and the rolling process as affecting the technical bottleneck of the mill, particularly, the innovation of the structures of the mandrel and shell charging/discharging equipment on the inlet table side of the mill, and the mandrel circulation process flow so as to substantially enhance the production cycle of the retained-mandrel pipe mill.