Different Scholars have different views of the definition of Discourse Analysis;it’s a research method that can be used by scholars with a variety of academic and non-academic affiliations,coming from a variety of disciplines,to answer a variety of questions.Critical Discourse Analysis is a branch of Discourse Analysis;this paper introduces its development,guidance theory and approach of it.As Positive Discourse Analysis is the extension of Critical Discourse Analysis,this paper introduces the production and main theories of it.At last,a comparison was made between them.