According to the social distance, relative power and the threat of speech act, both the speaker and the hearer can rationally choose politeness strategies to meet the needs of both sides。 According to the speaker and politeness to the hearer’s compensation degree from weak to strong were: public implementation of face threatening acts, positive politeness strategies, negative politeness strategy and the implementation of non-public FTAs and implementation of face threatening acts。 Face threatening act is a direct threat to the face of the strategy, usually used in emergencies, as well as the speaker's absolute power to the situation of the listener。 In emergency situations, the clear principle of transmitting information is far greater than the “Politeness Principle”, that is, the importance of information content is more than the way of information transmission。 Similarly, in the presence of a large gap between the two sides of the communication status and identity differences, the power of the party will rely on their own advantages to the other party。 Positive politeness strategy is to meet the listener’s desire to be recognized, respected and praised。 Brown and Levinson put forward fifteen kinds of positive politeness strategies, these fifteen strategies can have three kinds of understanding: the two sides have a consensus, the two sides have a cooperative relationship, meet each other’s wishes。 Negative politeness strategy is to show that the speaker will not interfere with the other party’s will and action, and fully protect the other’s private domain and the decision-making power。 However, the implementation of the sub threat behavior is higher than that of the above strategies, and the speaker's speech act is more ambiguous。 In this way, the speaker avoids the direct intervention of the hearer's actions, and also avoids the embarrassment of being rejected by the other party。 The intensity of these politeness strategies is as follows:

(Brown&Levinson 69)

Recently, some scholars have studied the application of politeness principles and politeness strategies in Business English correspondence。 Qin xiao jie (2001) has turned out the integration of business English correspondence by the analysis of principle and application of politeness strategies, and mutual cooperation between the two argument。 Si fu chen(2003) has studied the relationship between politeness principle and politeness phenomenon, speech morality, and the degree of performance of different language phenomena in business English letter。 Generally speaking, the writing of business English correspondence and politeness principle。 The research perspective of politeness strategy begins to show the trend of persification。

 the study of the principle of politeness in all countries, although it greatly promoted the communication between people, so that both sides can be willing to cooperate in the context of effective communication, the existing politeness principle is still not possible to cover all language communication。 Therefore, we are supposed to continue to explore politeness principles in-depth and research in detail。 The author sincerely hope that this article can provide some help。

2。 2 Studies on politeness principle in business letters文献综述

Business English letter belongs to the category of application text, which has its own unique language style and writing characteristics(Yang 101)。 In this case, the express of language should be specific and clear, simple and polite。 Therefore, in the writing of English letters, the writer should pay attention to the exact use of principle of politeness。 The language of the business letter is to convey all kinds of information so that it can establish a good corporate business image。

 Business English letters’ writing should insist on the correct principles and quality standards(Li 326)。 When you are writing business English letters, you should pay more attention to the content whether it is correct。 The writer must ensure the accuracy of grammar, punctuation and spelling。 In addition, due to the business information in business letters will be related to the economic interests of both sides, the writer should pay particular attention to the use of rigorous and accurate words。 Therefore, we should adhere to the principle of politeness in the business English letters’ writing, to ensure the authenticity and accuracy of all kinds of information。