Lexical ambiguity is a very common phenomenon in English and other language,which brings many troubles to people in communication.And that is also why people have deeply studied this phenomenon for a long time.This thesis makes a profound analysis of lexical ambiguity from semantic perspective.The thesis talks about the three sources that contribute to lexical ambiguity: homonyms,polysemy and word class ambiguity.Through the analysis of lexical ambiguity from semantic perspective,this thesis aims at helping people eliminate troubles in communication.