Al-Shaykh al-Saduq and al-Shaykh al-Mufid have played an effective role in the dynamics of Shia teachings by presenting ideas and innovations in hadith studies and theology. By preserving the epistemological realms of reason and narration, they considered both sources effective and necessary in religious knowledge and adopted different methods in using them; In such a way that al-Shaykh al-Saduq, with the predominance of the textual method, also used hadiths containing rational arguments, and al-Shaykh al-Mufid, with special attention to reason and rational approach, proved religious propositions and defended them. He has been interested in examining the document and the content of religious texts; However, al-Shaykh al-Mufid prioritizes the coordination of content of tradition with definite intellectual propositions over its documentary review. Despite the commonalities of these two theologians in the foundations and principles of religious beliefs, their differences can be seen in choosing the method of explaining and proving theological rules and teachings. Although in some fundamental differences, al-Shaykh al-Mufid 's rational method in examining the contents and documents of religious texts can be defended. In general, al-Shaykh al-Saduq's approach in paying attention to the narrative sciences can be considered as beginning of establishment of al-Shaykh al-Mufid 's rationalistic method and the basis for the development of rational sciences. In this research, an attempt is made to analyze the various dimensions and angles of epistemological and methodological differences in Sheikhin's theological approach with a comprehensive analytical-descriptive method, which is one of the innovations and advantages of this work compared to similar works written in this field.