Metalanguage is an important and universal language phenomenon in language communication. In Teacher Talk (TT), teachers will apply metalanguage consciously and unconsciously to interact with students through the adjustment of metalanguage in classroom communication. This paper discusses and interprets the functions, selection and adaptation of mata language in TT from the perspective of adaptation theory. The selection or adaptation of matalanguage in TT is for adapting to various contextual relations. In addition to the general functions of language, metalanguage in TT can also serve as the functions of code interpretation of target language, cognitive modeling, cohesive marking and other functions. English teachers should enhance their metalinguistic awareness in TT, and make good use of its special role in the English classroom teaching.