With the rapid development of international trade, business English plays a very important role in the global economic and trade activities. In business English correspondence, the effect of speech communication depends on the mastering and use of the politeness principle in large part. Business English letters as a means of communication,the guidance of the politeness principle is of great practical significance to establish a good business relationship, promote trade success. Therefore, it is necessary for us to study the politeness principle which is an important factors to influence international trade activities. With the rapid development of international trade, business English plays a very important role in the global economic and trade activities. In business English correspondence, the effect of speech communication depends on the mastering and use of the politeness principle in large part. Business English letters as a means of communication,the guidance of the politeness principle is of great practical significance to establish a good business relationship, promote trade success. Therefore, it is necessary for us to study the politeness principle which is an important factors to influence international trade activities.