In Xichang New Steel Enterprise Co.，LTD，in the production line of the narrow strip mill，the planed output was 200 thousand ton per year. However，after putting it into production in recent decade，the highest output was less than 150 thousand ton per year. After the two years transformation managed by the author，the real production increased constantly，and the highest output reached 670 thousand ton per year，the yield and the quality improved significantly. In this article，it mainly introduced the key part of the transformation of narrow strip mill production line—the roll system transformation of the narrow strip mill. At present，this technology has spread into many other factories，and it is regarded as the important technology and standard in the heavy machinery designing of the large strip mill production.