Business English letter is one of the most familiar mediums of international trade, is an important communication way to promote both sides of trade to understand each other's, also is the important tool of foreign economic activities. With the development of global economy, business English letter has become an important bridge to build a friendly relationship, develop business communication, and conduct business and trade activities.

1 Classification of Business English Letter

According to the contents of the letter, business English letters can be divided into inquiry letter, offer letter, confirmation letter, letter of notification, letter of payment, sales letter, refusal letter, invitation letter, thank you letter, letter of instructions, claims and claims, etc.. According to the nature of the information, the information can be divided into common news, good news, bad news and persuasive messages. (Stewart,1984:380-382).Good news business letters and ordinary business letter are often called routine business letters as well, including inquiry letter, order letter, letter of thanks, confirmation, payment letter; the bad news business letters contains harm to the recipient of information, such as refusing to establish relations letter, investment and litigation claims business letter warning letter etc.; persuasive business letters in an attempt to persuade the addressee, to write the letter, such as promotional letter cover letter and a reminder letter etc.. 

2 Basic Principle of Business English Letter

On the basic principles of Business English letter writing, Bobby D Sorrels summed up 6 C principles from one of his books, which called Business Communication Fundamentals. There are clear, concise, accurate, elegant and considerate and coherence (Bobby D Sorrels, 1984). On this basis, the domestic scholars have also been added and improved. Lu Mozhu(2001), Zhuang Xueyi and Zhou Yaozong(1998) as the representative of the scholars made today generally recognized business English writing 7 C principles, which are clear, concise, correct, specific, polite, considerate and complete.

2.1 Clear 

This principle includes two aspects, one is that the writer knows what he wants to write before starting; the other is the other side of the letter can completely understand the meaning that the writer expresses, will not produce misunderstanding. This requires writers have clear mind, clarity, accurate expression, and avoid using some vague and ambiguous words. 

2.2. Simplicity 

Simplicity refers to use the least language to express the most abundant complete content, and does not affect the politeness of the letter. Simplicity makes the letter more concise and powerful. English business letter whose form should be concise and to be point, language should be easy to understand, and content should be enrich and refining. This requires the writer in the process of writing as far as possible use simple, easy-understand, and simple words, and use a short and direct sentence. 

2.3 Accurate 

Business English correspondence is closely related to the rights, obligations, the interests, and the image of the company of the seller and the buyer. It is the basis for the production of all kinds of commercial documents, as well as the important documents to conduct business activities. Accuracy is the most important principle in business English letter writing. The principle of accuracy not only refers to the word spelling, punctuation, grammatical use, structural format, but also to ensure that the information involved in the letters, figures, facts and errors. Therefore, in the business English letter writing should be repeated review related information, for example: addressee's title, name, address, delivery time, and place, the quality of the goods, color, size, unit price, and total price. 

2.4 Concrete 

Concrete principle refers to the contents of the letter which is specific and true, whose information is detailed, rich and vivid and complete. In the process of writing of business English letter pay attention to avoid using general and vague expressions, such as, soon, at an early date, good, nearly and so on. For example: “I will send the price list to you soon.” and “I will send the price list to you after several days”, compared the two sentences, and you will find the first one is not good as the second one. If it can be more concrete it will be better, for example: I will send the price list to you next Friday.

2.5. Manners 

In order to establish and maintain a friendly trade relationship, business English letter in general should pay attention to courtesy, politeness. Politeness principle is not only reflected in the use of please, thank you, etc. these simple words and faces, but also reflected our country's foreign trade policy and diplomatic etiquette in between the lines, do neither overbearing nor servile, decent and generous. Specific politeness principle contains basic these several aspects: abide by international business intercourse practice; respect each other's customs, language expression be polite and have a sense of propriety, avoid using the command tone, with friendly, positive mood, try to use euphemism pointed out each other as people; reply to in time.

2.6. Understanding 

Consideration is to the other side of the interests as the starting point, standing on the other side of thoughtful, careful consideration of the problem in order to get the other side of the good impression and to achieve the desired purpose. The principle of understanding is a kind of technique to facilitate the use of transactions in business communication. 

2.7. Complete 

A complete business letter should detailedly answer to the question raised by the other party and express clearly the information of it. The integrity of the letter can help to establish a good corporate image, save the business contacts between the two sides to achieve the desired results, and avoid unnecessary disputes caused by important information.