Business English letter is an important component of external part of business activities,politeness of the language not only shows the high quality of the businessmen,but also helps to establish a good international business relations.From a stylistic point of view,business letters in English have their unique characteristics in accordance with the Politeness Principles (PP).A sufficient understanding of this theory and its corresponding features helps to write a neatly arranged letter which may bring about good business relations.Therefore,it is necessary to explore the language characteristics of business English letters on the Politeness Principles.This paper investigates the main characteristics of business English letters in terms of vocabulary and sentence features.The Politeness Principles are elaborated through the analysis of examples.Conclusions concerning the stylistic characteristics are drawn based on these analysis.By exploring these characteristics of business letters,the paper also provides the learners of business English with the techniques necessary for writing business letters.