Abstract:The concept "conjunction", viewed as a resource of cohesive devices and a topic of discourse semantic research in Systemic-Functional Linguistics, has its connotation and denotation extended to some extent.This paper discusses the connotations, denotations and classifications of conjunction, the basic units of conjunctive relations, the attributive relations of conjunction, and the transmutation of conjunction locating in the strata-the boundary of lexical and grammatical zones in lexicogrammar-the grammatical zone in lexicogrammar-semantics by reference to the researches done by the representatives in SFL.It also explicates the controversial and indeterminate classification-external & internal as well as the seemingly similar but different technical terms of explicit & implicit made by Halliday and Martin & Rose.All these reveal the research value of the transmutation of conjunction.