The history of Afghanistan-Pakistan relations shows that several convergent and divergent factors and components have been effective in the relations between the two countries for about 73 years. Therefore, the nature of the relations between the two countries has not gone through a steady process due to the existence of areas of convergence and divergence affected by these factors, and the relations between the two countries have always been based on chaos and tension, and this has caused the two countries to mistrust each other. Now, the Taliban regaining power, which Pakistan is one of its main supporters, could be the beginning of a new crisis on the relations between the two countries in the region in general and its impact on the security of the Islamic Republic of Iran in particular. According to this perspective, in the current research, the most important influencing factors in the convergence and divergence between the two countries of Afghanistan and Pakistan are analyzed on the one hand and the impact of their relations on the security of the Islamic Republic of Iran on the other hand. In fact, the purpose of this research, in addition to explaining the relations between Afghanistan and Pakistan, is to answer the basic question that Afghanistan's relations with Pakistan in general and considering the recent events and the Taliban's resurgence of power, what effect does it have on the national interest of the Islamic Republic of Iran? Based on this, it is hypothesized that the most important factors of divergence, border disputes, political structure and lack of strategic depth of Pakistan, and the main factors of convergence of the two countries are cultural-religious commonalities, economic and political cooperation. And due to the location of these two countries in the peripheral environment of the Islamic Republic of Iran, it is of special importance.