The conquest of Iran by Muslim Arabs is one of the most important developments in Iran's history. Iran was completely conquered over two decades and the Sassanid government collapsed. There are a lot of questions about this fall and the reasons for it. In this article, a new model is proposed to analyze the process of "Fotohat". The methodology of this research is library method that based on the main sources of conquests( Fotoh) in Iran. The main question is: are the conquests in Iran following a particular pattern and can we present it in the form of a theory? The second question is about how cities are conquered. Was it more than war or peace? In response to the above question, the hypothesis of this paper is formed. Iran is divided into eight regions. At the borders of these areas, we see the greatest resistance of the Iranian military and we call it "resistance at the border". After the border breaks,the advance of Muslim Arabs is more fast and less fight. As a result, the clashes are mostly by the military, and citizens are less at war. Understanding the speed and quality of conquests in Iran depends on understanding this pattern.