Critical discourse analysis is based on functional linguistics believes that there is an interactive relationship between the text and the context of the text. And the context of the text is affected by the context of situation. One of the discourse texts that has an organic and direct relationship with the outside world is Nahj al-Balaghah  that base on new theories of linguistics such as critical discourse can discover the unspoken hidden behind its textual context. Imam Ali (AS) tries to confront her opponents by using an enlightening critique of the ruling ideology To change the cultural context of the society in line with the lofty goals of Islam And examining the attitude of Imam (AS) through the lens of critical discourse helps us To understand how the Imam uses language in order to confront oppressive discourses. This research is done by analytical-descriptive method and base on Norman Fairclough theory and Examines how Imam Ali's (AS) discourse interacts in three levels of description, interpretation and explanation. Examination of sermons and letters in terms of vocabulary and grammar showed that Features of Fairclough approach there are in the context of empirical, expressive and relational values in these sermons and letters.. At the level of interpretation we saw that his discourse is in line with the political and social atmosphere of that time. At the level of explaining ideology behind the Imam's discourse is defending his own legitimacy and the non-compliance of justice in her right.