Abstract: This paper first explores the basic rules of language as well as the origin and development of vague language. Then the paper explains the definition and characteristics of Business letters and shows the principles which are needed to direct this kind of communication. In the following part, an introduction is given to show the origin, definition and the ways how vague language is used. Vague language is employed in business letters to deal with four circumstances. And it does have five functions which can affect a lot in business. At last, the analysis and conclusion of using vague language in business letters is given.
Key words：Vague Language; Business Letters; Politeness Principle