There are many kinds of tools for human communication, but language is the most common, direct and effective one. In any form of language communication, there are primary discourse and meta-discourse involved in. Nowadays, more and more research scholars have paid their attention to it, and it has become one of the focuses of discourse analysis. In this paper, it gives an overview of the origin, definitions, functions and classifications of meta-discourse, and also the prospects of the future research are put forward.