In 1972, Selinker proposed the concept of interlanguage, an unique language system for second language learners whose language forms are transforming between target language and native language. Through interlanguage, teachers not only can investigate the development stage of learners' language, but also can assess and adjust learner's interlanguage. By adopting the circle of pedagogical strategies- outputting, feedback, and corrections-, teachers can assist learners to develop native-like language. Mostly the previous studies focused on the interlanguage's correction strategies which refer to the methods and timing of giving feedback, and hardly examined how language teachers interpreted interlangauge before giving feedback, and how to develop the capability of understanding interlangauge. Through classroom observations, researcher of the study find that novice Chinese teachers' capability of comprehending interlanguage is not mature enough. However, it is not easy to develop teacher's ability by lecturing, but arranging proper training procedures. Thus, the objective of current study is to develop the student teachers' capability of understanding interlanguage at Introduction of Teaching Chinese as a Second/Foreign language, an undergraduate required course. Sixty-one student teachers participated. Through an action research method to connect theory and practice, this training course developed a training procedures containing cognition, field practices, and reflections. Results showed after one semester's training, student teachers' professional knowledge on recognizing interlanguage has been promoted, which can be treated as a reference for teacher trainers to develop a program.