Critical Discourse Analysis(CDA)first put forward by Fowler,Hodge and Kress inLanguage and Control(1979)is a method to study the relationship between language powerand ideology.It seeks through the minute details of linguistic structure in the light of thesocial and historical situation of text to display the value,belief and ideology which areencoded in the language and which are invisible by most people.　　 The performance of CDA is based on Hallidays Systemic Functional Grammar(SFG),which proposes that language as the product of social process can both reflect and influencethe society.Halliday considers that language as a social signal system can express meaningsin the social and culture background.Almost every culture in the world can be found out thegeneral metafunctions,i.e.,ideational function,interpersonal function and textual function.That is the Hallidays three metafunction of language.In Hallidays point of view,thediscourse is the basic unite in peoples interaction.Out of the similar idea of discourse andHallidays detailed and specific analytical approach of language,SFG is taken by criticaldiscourse analysts as the theoretical and methodological base of CDA.　　 The present thesis picks up the 44th American President Barack Obamas speech onracial issues as the critical study object.In the beginning,the thesis begins with a briefintroduction to the general background of the material and the reason of choosing it as studyobject.It also provides detailed description of its theoretical principles:Hallidays SystemicFunctional Grammar which is the guidance of analyzing process.　　 The uniqueness of the thesis lies on the corpus--Barack Obamas speech on race issueA More Perfect Union.It is well known that in America,racial issues are historically subtleand complex,especially the relationship between White Americans and African Americans(also black American in this thesis).After the dream of first black president came true,Obamas speech on racial issues which won him most votes in Pennsylvania is worthstudying.The present study analyzes the speech from Hallidays three metafunctions,todisplay Obamas application of language strategies; and explains the purposes of applyinglanguage strategies from social and historical factors.　　 From the study the author finds that Obama preferred material process,which tookadvantage of Americans desire for governments actions to change stagnant economy andunsteady social situation.He frequently used the first personal pronoun"I"to show that he isthe one who stands on the side of the people who call for change and hope for a fairer andmore democratic world.However,he used much more low value finite operators to statespecific racial problems so as to avoid answering the sensitive questions directly and makingclear his specific plans.　　 Through the study,the author makes the conclusion that Obamas speech on racialissues,and his effusive words which express his opinion on this topic are not so encouragingand positive as many audience thought.Race is just once more manipulated by politician toconfuse supporters and voters.In addition,the finding of the study suggests that moreattention should be paid to the statements of the so-called"the history rewriters".Surfacelanguage meanings cant be considered as a standard to judge speakers ideology andpurpose; however language structures can do that.This thesis once more reminds us that weneed strengthen our critical consciousness so as to distinguish what is right and what iswrong.