Population and family satisfaction are fundamental components of national power and the determinants of national security of any country. Its development process, direction, and level are a function of the population. The aim of this study is to analyze the impact of the country's population decline and the aging of the age structure of the Iranian population on the country's national security. The theoretical framework used in this study is a combination of Morgenthau's theory of national power, Buzan's existential security, and Frank Nothestein's demographic transition. In this study, demographic changes are considered as an independent variable, and the effects of this phenomenon in three areas of hard power, namely the country's economy and defense strength, soft power (national identity and cohesion), and human capital, and their impact on national security, have been examined. The hypothesis of this study is that the quality and pattern of human life are also constantly changing and evolving due to the modernization of human nature. Population, considering national characteristics and traits, is an effective factor in assessing the power and security of the country, and its political effectiveness can also be examined in the field of politics. Findings show that the decline in Iran's population growth leads to weakening economic growth, reducing the country's defense capacity, reducing technology production, productivity, and weakening the country's national cohesion and security. The present research method is descriptive-analytical, and the method of collecting information is the use of library resources and document review.