This paper investigates the effects of debt, firm size and liquidity on internal resources as well as investment expenses on 140 selected firms listed on Tehran Stock Exchange over the period of 2006-2010. The survey has performed based on panel data analysis and the proposed model uses Husman model chooses random effect as well as fixed effect to analyze the data. The results indicate that there was a positive relationship between firms’ debt and sensitivity of investment-cash flow. There are also some positive and meaningful relationship between firms’ size and liquidity on one side and sensitivity of investment-cash flow.