From the Constitutional Revolution till the Islamic Revolution, the Iranian society witnessed a great deal of political turmoil, vast and successive unrest in the realm of the politics. Enquiry in the nature of the relation of these events with the complexity of the social structure of the country, forms the focal point of the present study. In our study of the social structure, despite focusing into the social classes, and the emerged gaps between the different social groups and the effects of ethnic and regional cleavages in the evolve of political crisis during the events of Mashrooteh, the article also considers the rise of Reza Khan, the nationalization of the oil industry and the Islamic revolution.The article argues that the study of the formation of the successive political unrests in the country should be connected to a multi-layer social structure and its related political ideologies. Thus, the article also focuses on the nature of the populist .movements of this period while keeps its relation with the social structure in the mind. These events could not happen if the cleavages in the social cohesions did not lead to the gaps in the organically established relation which used to canalize the relation in and out of the classes. A fast review of the social changes and class relations in Iran shows that due to the fast economic and cultural changes, in several points during this period, the social gaps and breaks have occurred. The developments of these social cleavages were the main ground for the occurrence of the populist movements during the concerned period of this study.