Iran economy is a dependent economy on exogenous factor of oil revenues and as Iran economy is governmental condition, the production quantity depends on this exogenous factor and always has lots of fluctuations. As lack of fluctuation in production quantity and its continuum growth form the increase in profitability expectation of private investment, this article reviews the effective factors on private investment focusing on fluctuation of real quantity of economy using time-series statics between 1966 and 2011. At first by the Generalized Auto-regressive Conditional Heteroskedastic (GARCH) fluctuation of the quantity of economy is calculated then, by using the Auto-Regressive Distributed Lag Model (ARDL), model is calculated. The results reveal that in long term and short term fluctuations of country’s production have a negative effect on private section’s investment. Reviewing of other factors shows that private investment has a positive relation with both gross domestic product and production capacity and also has negative relation with exchange rate and long term deposits.