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

摘要：本文首先阐述了一下，有关于语言，尤其是商务信函语言的基本原则，同时介绍了模糊语的起源和发展。接下来，首先介绍了一下商业信函的定义，特点以及其重要的几个原则，包括精确原则。然后介绍了模糊语的起源，定义以及及其商业信函中的两个重要功能。随后分析了商业信函中模糊语的使用的五种场合，并分析了模糊语的几个语用功能。最后，对模糊语的在商务信函中的使用及其注意事项进行总结。

关键词: 模糊语言;商业信函;礼貌原则