Population growth and the level of fertility and the relationship between them and socio-economic development in different countries, especially in developing countries, are the major interests of today's sociologists and demographists, in particular the case of Iran. Method: In this article, the combination of two methods, Literature Review and Further Analysis, were applied, and population data and statistics were gathered from UNPF, UNICEF, World Bank, ...and, the relationship between the variables were analyzed by using SPSS. Findings: Research findings show that the higher the level of development, the lower the level of fertility, and population growth. The best pill for contraception is economic development. Results: The relationship between the development and fertility rate is reversal, it means that, in world's deprived regions, with the same level as Iran, and in country's provinces, this relationship is so obvious.