Abstract: Nowadays, British English and American English languages are likely to be more and more close to each other. It is because British English has tended to be close to American English. However, there are still many differences between British English and American English, which create misunderstanding and inconvenience during various types of communication. In order to help both native and non-native English speak to avoid those issues, this thesis, introduced some important differences. In addition, the presenting paper also discusses the original and the development of those differences. This includes both linguistic theoretical frame work and daily application in business English writing. Furthermore, this paper also predicts the further development of British and American English.  

　　 American English is a branch of British English which formed many features that is obviously different from British English during a long time development. In many aspects, such as words, pronunciation, grammar and expressions their difference is obvious and especially important in business English writing: a small mistake or wrong expression might create a great misimpression and cause huge loses for an international enterprise.    

　　Culture difference is the first fact that causes the difference. Comparatively, British English is more formal. Since the United States of America is formed by immigrants from all over the world, especially from England, the characteristics of American are enthusiastic and humor. The features of American English are therefore influenced by American people. It is lively, relax, free and tolerable. British English and American English were developing in different phenomenon in two hundreds of years. Although the changes are slow, there are obvious differences in many aspects such as words, spelling, and pronunciation.

   Although there is personal preference—some like American English and others prefer British style. Compared with British English, American English is more convenient to people, and more likely to be mastered by people. However, some people prefer British English because it is more official. More importantly British literature left deep impress on English and the entire western culture, its influence will be persisted. 

　　Just like the isolation of species create new sub species; it is the isolation of people creates the sub type of language. However, because the the radical development of communication technologies, the relative isolation between American and British is fade away. As a result, British English and American English will have having a tendency to affect each other and British English tends to be close to American English. A reasonable predication will be, at least in daily, two branch of English will became more and more similar, until they reach an equilibrium point that the power of culture difference (which keep language unique) and the power of culture influence (which make language similar) are balanced.       

Key words: difference; cultural cross; develop; variant; preference; advantage