「七字調」是歌仔戲唱腔中最主要的曲調。其音樂除了在板式上呈現多重變化之外，亦可從其豐富的調式變化中，觀察其音樂色彩，研究其如何以調式變化營造戲劇效果等現象。並在其調式色彩的演變中，探討其衍繹發展，這牽涉到其他劇種對歌仔戲之影響及伴奏樂器的演奏造成唱腔調式色彩變化等相關問題。本文試圖以「七字調」為中心，研究其調式之基礎理論與戲曲中之實踐，論述方式採音樂分析及現象探討兩面向呈現。

　　　　　“Seven-word song” is one of the major tunes in Taiwanese Opera. Besides observing its various rhythms, we should not only pay attention to the characteristic of the music, but also study how to create dramatic affects and other phenomenon from the copious mode changes. From the development of the mode character we can discuss the subject of evolution of the music. Moreover, we can study the subject of the effective of how the other kinds of drama affect Taiwanese Opera. In addition we can examine how musical instruments affects the development of song's mode. This article is based on “Seven-word Song” to study the basic theory of the mode and the practice of the opera. The study employs both musical analysis and phenomenon discussion to present the issue.