Abstract: This paper contrastively analyses the characteristics of formal and informal languages in Business English letters. In the study, this article specifically compares the two main aspects of formal and informal languages from the point of lexis and syntax in business English letters. The article analyzes the differences in wording choosing and wording expression, from the perspective of vocabulary. It analyzes the differences in sentence structure and special forms of expression in sentence, from the perspective of syntax.  The aim of the study is to help students and businessmen write high quality business English letters and to achieve effective business communication by business English letters. 

Key words: Business English letters; formal language; informal language; contrastive analysis

摘要: 本文采用对比分析的方法，分析商务英语书信中正式用语与非正式用语的特点。在研究中，本文从商务英语书信中的词汇和句法两方面对比正式用语与非正式用语在商务英语书信中的运用，其中在词汇方面分析两种用语在词汇的选择以及词汇的表达上的差异，在句法方面分析两种用语在句子结构和句子的特殊表达上的差异。研究两种用语的特点，目的是帮助学生和商务人士写出高质量的商务英语书信以及更好的通过商务英语书信来实现有效的商务交流和沟通。

关键词：商务英语书信；正式用语；非正式用语；对比分析