Media of instruction is the language teachers use in classroom teaching.It is an important reference index used in English teaching process.Shall we only use target language as media of instruction in our foreign language teaching? Or shall we also use mother tongue in a timely and moderate way? It is a question of great concern for each foreign language teacher.This paper,therefore,based on the summary of relative theories and case study results in corresponding fields and on the actual practice of our own school,attempts to consider and study the above questions.