With the victory of the Islamic Revolution of Iran and the emergence of a new system in the international arena, theorizing about Islamic government in the jurisprudential – political thoughts of Shiites became an important issue. (History) Of course, various groups inside and outside religion face many challenges and the origin of the legitimacy of the Islamic government is from these important challenges. (Problem) Ayatollah Mesbah Yazdi is from the very few people that have investigated the issue of the origin of the legitimacy of the Islamic government. But, the roots of the formation of his thought about the legitimacy if government at the time of the Occultation of the Infallible Imam (Aj.) is not investigated using metatheoretical method so far; (Background) therefore; the main question of the present paper is that: what are the roots of the formation of the theory of legitimacy of Islamic government in the political thought of Ayatollah Mesbah Yazdi? (Question) It is assumed that the roots of the theory of the legitimacy of government in the thought of Ayatollah Mesbah Yazdi are influenced by four social-inside, social-outside, intellectual-inside and intellectual-outside factors. (Hypothesis) The present paper tries to explain the role of these four factors in his viewpoint; (Objective) to reach this goal, the metatheorizing theory of Ritzer (MU kind) is used. (Methodology) Proving this point that the theory of Ayatollah Mesbah Yazdi is independent from political wings is the most important achievement of this paper. (Findings)