Abstract:The correct choice regarding phrase and sentence is the basis of courteous language used in English business letter writing, just like the qualified bricks for a strong building, providing basically courteous language tone for the entire letter.

　　　The first part of this paper is the introduction of the development of Politeness Principle, the significance and the purpose of the research. In the second part, English business letter’s definition and its relation with politeness are elaborated. In the third part, this paper exemplifies the choice of decent words, tense, mood and sentence structure in courteous business English letters. The fourth part of this paper analyzes the application of Politeness Principle in complaint letter, claim letter, the urge of payment letters, introduction letter, the refuse of request letter, promotion letter as well as on the basis of the examples, and attempts to adopt a approach of comparison on the research, in the hope of providing guidance to the English business letter writing. Appropriate words and sentence help writer write a decent, courteous business letter, which increasing transaction volume in the course of business negotiating.

Key words: business letter; Politeness Principle; courteous language

中文摘要:商务信函写作中礼貌词，礼貌句的正确选用，词语, 句子是整篇信函基础，就像整栋大楼的砖头一样，为整篇商务信函提供了基本的语言基调。对礼貌现象的研究一直是语用学感兴趣的话题之一。本文第一部分介绍各语用学家对礼貌现象的研究，第二部分概述如何用正确的词和句式来体现礼貌，第三部分着重探讨语言学家利奇提出的礼貌原则在不同商务英语信函文体的运用情况。恰当运用礼貌词，礼貌句式和礼貌原则有助于信函作者写出得体, 礼貌的商务英语信函,获得期望中的效果,从而实现商务活动中的双赢。

关键词：商务信函；利奇礼貌原则；语用学；礼貌词