Abstract: With the rapid development of economic globalization, business English letter has played an important role and has been an indispensable tool for us to exchange information in the business affairs, which is an important approach for international trade. A good business English letter cannot exist without politeness. Firstly, this paper introduces the current study of business letter and describes the seven writing principles in business letter, secondly, it focuses on Leech’s Politeness Principle and gives examples and analyzes the application of tact, generosity, approbation, modesty, agreement and sympathy maxims in business English letter. Furthermore, politeness can also be expressed by the usage of positive words, vague wording, the euphemistic way and you-attitude, etc. in the letter. In a word, politeness principle plays an important role in the current business letter. A refined and courteous business English letter can enhance trust between both parties of the trade and improve the possibility of the win-win success of the trade activities. 

Key words: business letters; politeness principles; application 

摘要：随着经济全球化的迅速发展，商务英语信函在商业事务中占据了相当重要和不可或缺的地位，它是进行国际贸易的重要途径，但一篇好的信函离不开对于礼貌原则的遵循。本文首先回顾了商务信函近来的情况，叙述了信函的七个写作原则，然后重点从利奇提出的礼貌原则出发，通过列举实例，主要分析了商务英语信函中得体，慷慨，赞扬，谦虚，赞同，同情准则的应用。此外，信函中的礼貌还可以通过肯定性，模糊词的使用，委婉性，尊他性等来体现。总而言之，礼貌原则在当今社会的商务信函中还发挥着举足轻重的作用, 一封很有礼貌的商务英语信函，可以增强贸易双方彼此之间的信任感，从而提高商务活动双赢的可能性。 

关键词：商务信函；礼貌原则；应用