Abstract: Studies on readability in America date back to the early 20th century, when Thorndike^[1] the phycologist published the first book in which English words were arranged in accordance with their frequencies.This set a trend toward researches of this paradigm based upon words as a variable.As yet, readability researches have been continuing across the world.Fathered by M.A.K.Halliday, systemic functional linguistics(SFL) is a powerful linguistic theory widely used to solve language or language-related problems.Readability is not an SFL concept, so researches in this regard represent a new perspective.To fuse the concept into the theory, this article first tries to capture the essence of readability through revisiting such aspects as its definitions and dimensions, influencing factors, and the traditional approach to it;and then goes on to discuss to what extent SFL can expand the scope of readability studies, with reference to Halliday's accounts of“meaning”, and of the three orientations of the theory in the early 21st century.It is concluded that readability and SFL are complimentary in that the latter provides a theoretical framework for the former, while the former broadens the research scope of the latter.Future explorations will serve as a touchstone of the validity of SFL as a general theory of language, an appliable linguistics, and a general theory of meaning or natural science of meaning.