In this article, the author is to comparatively investigate one of the common issues of law system for the two countries of Iran and America i.e., the commonalities and contradictions regard with the method of setting of institutions, powers and their quantity. In this regard, it will be briefly investigated the structure of power or the power distribution pattern in the two countries of Iran and America. The political system of America is of federal type; accordingly the distribution of power would be discussed once among the central government and states, and the other time among the three powers in the level of federal. In the Islamic Republic of Iran, which is of a concentrated, non-federal and political system, the pattern of power distribution would be investigated in the mould of four axes, i.e., leadership institution, legislative power, executive power, and judicial power. The commonalities and contradictions of the two accepted patterns would be exhibited via the structure of power in two countries.