Language is a very complex and great invention.Human beings are capable of making all kinds of sounds through the close cooperation between speech organs.Without making speech sounds,we cannot communicate with other people effectively and easily.Therefore the enthusiasms for phonetic study have never been interrupted.Coarticulation and assimilation were discovered in the 1960s.Since then,they have become a hot and difficult topic of the speech research.Until now,different definitions of coarticulation and assimilation have been provided by many famous phoneticians.The overall objective of this study is to unscramble the concept of coarticulation and assimilation.In addition,the author tries to give her own analysis of these terms through presenting daily examples.