Abstract: Summarized in the paper is the general principle for designing the pass of the 2-roll rotary piercing mill,and also set up are the theoretic system and specific calculation method for design and adjustment of the piercing mill.And the effectiveness of the design is validated with actual examples so as to promote the piercing process to develop in a theoretic and quantitative way,instead of the present empirical and qualitative way.The research result reveals that the roll space is a critical parameter for evaluating the design and adjustment of the piercing-roll pass;the roll space can be increased by means of enhancing the secondary bite ability so as to improve the piercing quality;it is regarded that with the roll space and the feeding angle remain unchanged,keeping a large contact area between the piercing roll and the billet is a much better design;the principle of minimizing the free deformation zone length should be satisfied through adjustment of the rolling mill proper during the piercing operation;and the plug diameter plays a key role in determining the outside diameter of the shell.