Despite a voluminous literature addressing English language teaching, the explorations focused on knowledge-building are rather limited in number. This is particularly the case with China's tertiary English education. Unlike existing research, this study investigated Chinese college English teachers' knowledge-building about rhetorical figures by drawing on the ideas of Autonomy and Semantics in Legitimation Code Theory. Designed as sequential mixed-method research with a development purpose, the study takes as its analytical data the pedagogic discourse generated in the finals of China's National College English Teaching Context. It was found that the knowledge practices about rhetorical figures vary, for one thing, in their likelihood of shifting to introjected codes and returning to the initial sovereign code and the motivations for their possible drift into exotic codes; and for another, in whether they are unpacking-oriented, repacking-oriented, or unpacking-and-repacking-integrated. With this, the study demonstrated how varied knowledge practices in English language teaching or English-medium teaching can be portrayed, distinguished and explicated in terms of autonomy and semantic code shifts and by reference to their display of autonomy pathways and semantic profiles. The study also makes contributions by actualizing the perspectival complementarity between Autonomy and Semantics in describing and interpreting pedagogic practices, shedding light on the design and improvement of knowledge-building in both English language teaching and disciplinary teaching, and highlighting the necessity of developing non-native English teachers' metalinguistic awareness of Legitimation Code Theory and systemic functional linguistics.