The World's Fair is an exceptional phenomenon in history that began in the midnineteenth century in 1851. This event (as the collective heritage of the whole of humanity) has evolved over time under the shadow of global patterns and according to the general trend of the world. In the historical review of the World's fair, there is a gradual change in its main goals; In a way that today, by moving away from the original goals or at least diminishing them, according to the experience of our time, has become a more global event. Although technological advances have played a major role in the World's Fair since the Industrial Revolution, these events have always reflected specific periods in history. Such developments in world’ s fairs have not taken place according to a pre-designed process; Rather, given the progress, conditions and atmosphere of the international community in each period, it is happening. In addition, in the history of the World's Fair, the goals, programs, features and in general the process of presenting architecture have undergone fundamental changes. To the extent that in some special works and periods, the design of pavilions has been used as a tool to present new architectural styles and approaches. However, very limited research has been done on the evolution of world's fairs, especially in the field of architecture. The study of architectural developments in the history of world's fairs allows the formulation of paradigm shifts in different periods. In this regard, the present study in a qualitative format, Analytically-explanatory method and with library studies, tries to provide a clear path of architectural developments of world's fairs by examining the participating pavilions and also explaining the historical periods of architecture in this event. The results show that the architecture of the pavilions, with regard to similar features, illuminates special historical periods that are appropriate to their content; In the present study, they have been analyzed, reviewed and organized. Despite the many differences and variations in the presentation of the pavilions and the various purposes of the fairs, a coherent content can be provided to define each specific period in the architecture of this event. World's fairs in the course of the architectural developments of their pavilions, have wide and varied aspects and different approaches, but an attempt has been made to present a specific trend in each of its explanatory periods, in general. The content of each of these periods depended on the circumstances of the world community, as well as the general programs and strategies considered in the world's fairs. Four historical periods have dominated the approaches and strategies of architectural design of the World's fair, Which include the following: 1. Scientific and technical innovations in construction in pavilions (1889-1851), 2. The combination of industry and art and the use of emerging styles and various historical references in the design of pavilions (1939-1893), 3. Utilizing the latest structural achievements, new building materials and structures to solve global problems (1970-1958) and 4. Pursuing sustainable architectural approaches (1992-1995).