Teaching and learning is a process in which learners and teachers interact with each other. During this process, the language used by L2 learners has been defined as “interlanguage”. Nevertheless, how to define the language used by L2 teachers? To this issue, there is a ready terminology in ideological resources of Chinese, that is “Jie Yin”. “Jie Yin” contains the meaning of “meeting” and “guidance” in Chinese. Meeting and guidance are not only an innate metaphor of the relationship between L2 teaching and L2 learning, but also a vivid portrayal of the process between L2 teaching and L2 learning. In this study, we use “ferry language” to indicate the language used by L2 teachers for meeting with and guiding interlanguage. With regards to L2 learners, ferry Language signifies learning resource which is a combination of medium resources, objective resources and affective resources. While with regards to L2 teachers, ferry language means accommodation and improvement for students. The accommodation of L2 teachers can be categorized into modality accommodation, code accommodation, audiovisuality accommodation, structure accommodation and culture accommodation. The improvement contains model improvement, expansibility improvement and motivation improvement. The evolution of ferry language implies a weaker accommodation degree but stronger improvement power. Using interlanguage is an inevitable process for L2 learners, whereas it is an active and conscious design for L2 teachers. It should be noted that interlanguage and ferry languageare mutually generative. Specifically, interlanguage develops when meeting with ferry language and being guided by ferry language. Additionally, ferry language evolves with the development of interlanguage. Therefore, the study of interlanguage can improve the meeting and guiding competence of ferry language, while the study of ferry language can also promote the advancement of interlanguage’s conversion velocity.