Halliday^’s systemic functional theory is one of the most important theories in text linguistics that cateres to formation of language and texture of text and forms. It is based on three meta functions: ideological, interpersonal and textual. This theory is considered a suitable model for the stylistics of text discourse and it can help to understand all aspects of author's discourse style. The present research was investigated with an analytical method and systemic functional linguistics approach on 42th sermon of Nahj al-Balagha based on the ideological and textual meta-functions in order to achieve the imam's discourse style and deeper understanding of the subtleties and hidden values ​​in the sermon. The results showed that the extent to which imam uses all kinds of processes is in harmony with the content of sermon and because of the content of sermon, which is related to mental affairs such as following the passions and long wishes, and knowing the most important differences between this world and the hereafter. Mental processes (0.050) and relational processes (0.031.25) have the biggest role in shaping the discourse of the sermon. From the point of view of textual meta-function, imam has expanded the concepts of sermon using structural factors (composite initiator (0.088), mark (0.075), creating new and old information (0.050) and has created a coherent connection between different clauses of the sermon by applying techniques of non-structural factors, grammatical, relational and vocabulary coherence. In fact, imam has established discourse style of the sermon according to the situational context and his knowledge of the audience to prevent their pride and sense of worldliness after victory.