Abstract: Elaborated here in the article are the rolling process of the Φ168 mm PQF pipe mill,and the workflow of the mandrel-retaining holder.And also analyzed are the design of said holder's original 5-linkage mechanism,and the shortcomings thereof.Accordingly the modification plan for the said holder is proposed.It is regarded via the analysis that the bottleneck problem of the said mill that the production cycle and the equipment running efficiency are restricted has been completely solved owing to such actions as modifying the case structure,the middle linkage rod and the support seat of the 5-linkage mechanism,and changing the mounting type of the holder locking hydraulic cylinder,etc.As a result the continuous production consistency and the equipment operation rate of the production line are both enhanced.