This paper describes the structure characteristic about skin pass mill introduced from abroad in a large steel mill， elaborates steel tension， rolling force and elongation control principle and basis; introduces the hydraulic control principle， as well as the“constant elongation” and“constant rolling force” two control modes; some prob- lems and solutions from the localization process and debugging stage are summarized， and an example is given to il- lustrate the good use of effects of the skin pass mill.