Capital structure is the issues that accepted companies in stock market have confronted for determining the optimum volumes of debt, and investment in the capital structure regarding minimizing costs and increasing stocks value. in this study, the effect of some characteristics of company such as, the size of company, asset structure, profitability, expected growth, ratio of interest rate coverage cost, immediate ratio, and assets return in determining company's capital structure are studied to help business managers, investors, loaners using the results. For this purpose 132 active companies in negotiable papers exchange in Tehran have been chosen as samples, mixture of interval data and time Series (merged data) were used. Using econometric methods like panel data, the relationship among variables is evaluated and tested. To estimate the model, first F-Test, Hasman-Test are carried out to choose the best model from ordinary panel data, fixed effect and random effect by using E-views and Excel software. According to research findings, there is a negative and significant relation between the companies’ capital structure and the assets structure, profitability, expected growth, their immediate ratio and assets output (outcome), and there is appositive and significant relation between the companies’ capital structure and the companies’ size and the ratio of expenditure coverage.