Abstract: This thesis mainly discusses the application of the six maxims of Politeness Principle, proposed by Geoffrey Leech, in business letter. In the thesis, the author first introduces the definition and function of business letter, followed by the introduction of the Politeness Principle.  Then the thesis discusses the application of Politeness Principle in business letter. Through the discussion, the author finds that the six maxims are usually observed in situations like giving orders and promises, requiring price and negotiating condition, apologizing for and admitting mistakes. By following the six maxims, negotiators can reduce the differences and build friendly business relations through business letters. 

Key words: Politeness Principle; business letter; application

摘要：本论文主要讨论了杰弗里·利奇提出的礼貌原则的六个准则在商业信函的应用。本文首先介绍了商务信函的定义和功能,其次是礼貌原则的引入，然后本文讨论了礼貌原则的应用在商业信函。通过讨论，作者发现人们通常是在下订单、承诺、征询价格和谈判条件、承认错误和道歉等场合遵循礼貌原则的六个准则。谈判者若能遵循六个准则，便可在商务信函中减少谈判双方差异，建立友好地商业关系。

关键词：礼貌原则; 商务信函; 应用