本文以「北曲尾聲曲牌的重要性」為思考的出發點，透過《北詞廣正譜》與《太和正音譜》、《九宮大成北詞宮譜》、《北詞簡譜》、《北曲新譜》前後諸曲譜的比對校雔，觀察其格式上的衍變異同，歸納出《廣正譜》所收北尾，各宮調實有其堪為尾聲原型之正格曲牌，以此基本類型為基礎，進一步衍生變化為三種類型－鎔鑄集曲而成、正襯增減變化、出入宮調使然，以及綜合上述三種之複合式變化，因此形成琳瑯滿目的尾聲曲牌。進一步觀察這些北尾的來源出處，以及李玉十餘部傳奇作品中所運用的北曲尾聲曲牌，發現李玉兼收諸宮調、元明散劇曲，呈現出北曲吸收諸宮調時變化移異之跡；而其劇作運用與後世崑曲舞台所流行者，多有集中在少數幾曲的情況，和上述釐清體系之後的北尾曲牌不謀而合。因此，李玉《北詞廣正譜》顯得尾聲曲牌變化紛雜，恐怕是曲家為了盡力陳述與完整表現出由牌格式實際演變的各種可能狀況，其力求完備之態度雖值得嘉許，卻難免於繁瑣凌亂之譏。由此可知，北曲從元代到清代、從大漠漢北一路輾轉綿延到水鄉江南，時移世異之下，清初戲曲家所認知的北曲已經產生了實質上的變化。

Focused on the importance of qu pieces of northern qu music's final movements, this paper compares and contrasts the ”Beiciguangzhengpu”, the ”Taihezhengyinpu”, the ”Jiugongdachengbeicipu”, the ”Beicijianpu”, and the ”Beiquxinpu”. Every qu pieces of the final movements collected in Qing scholar Li Yu's ”Beiciguangzhengpu” has its prototype qu piece; the diverse qu pieces are actually formed through combination, addition, subtraction, or variation of the prototype pieces. The origins these qu pieces and the qu pieces of the final movements in Li's chuanqi works prove that northern qu undergoes transformations with time and that Li assembles not only northern qu pieces but different qu pieces and Chinese opera pieces in the Yuan and Ming Dynasties. The condition of these qu pieces agrees with that of Li's Chinese operas and the few Kunqu operas that catch on after Li dies. The changes of the northern qu final movements are in fact made only for demonstrating all the possible changes of qu pieces. Li's pursuit of perfection is commendable, but it also makes his ”Beiciguangzhengpu” unsystematic and disorganized. The northern qu that the early Qing opera experts recognize, after traveling from the Yuan to the Qing Dynasty and from the northern to the southern China, has actually gone through essential changes that make it different from northern qu's original appearance.