Issues of interest rates have been one of the most controversial economic issues. Thus, the role of interest rates in the economy and its impact on economic growth in the economics is the most important. Such that different scholars have different perspectives on it. Thus, Theories studied in the economic literature on interest rates is very important. This article is based on existing theories and using mathematical models, Attempts to analyze the causes and effects of the monetary interest rate. This paper uses LIZREL software and during the period 1972-2011 in Iran's economy performed. The results indicate the monetary interest rate has a negative effect on economic growth.