Abstract: Business English letter is an important part of business activities. The language of it not only shows the high quality of the businessman which may contribute to the success of the business, but also helps to establish a good international relation. Therefore, according to the politeness principal, it is necessary to well-arranged the language. This paper analyses the politeness principle in business letter from three aspects: language expression, content expression, response expression. By exploring these characteristics of business letter, the paper provides the learner with necessary techniques for writing business letters. 

Key words:  politeness principal; business English letters; lexical and syntactic characteristics; content of letter; response of letter

摘要：商务函电在现如今的国际商务活动中有着举足轻重的作用，礼貌的函电语言不仅能够取得对方好感赢得对方信任，最终促成交易的达成，而且也能够展示良好的企业形象，促进建立企业间良好关系的形成。因此本文将主要从三个大方面阐述如何在商务函电中礼貌的表达。第一方面从词汇和句型方面讨论，第二方面从具体内容方面讨论，最后一方面从具体回复途径和注意事项方面讨论。

关键词：礼貌原则；商务函电；词汇句型；具体内容；具体回复方式