Among the main languages of the world,English has the largest vocabulary,though its history is comparatively short.The 20th Century witnesses the fastest increase of English vocabulary.Vocabulary is a sensitive element in the language,keeping a record of its development.This paper attempts,in the time order of newly coined words,to trace the development of the 20th Century's English vocabulary,from the perspectives of contributing factors and developing modes.The paper aims to describe the trends in English vocabulary development and help in English vocabulary acquisition.