The experimental measurements of the optical thickness of the cesium atom vapor interacting with the lights of different intensities and polarizations at different energy levels and temperatures are demonstrated. The rate equations of each Zeeman sublevels are established theoretically and the numerical solution of time-dependent absorption coefficients is obtained by solving the rate equations with Runge-Kutta methods. The average absorption coefficients at resonant frequency can be calculated by numerical integration because of the effects of the thermal motion of atoms and beam width. The fitting of transmission spectrum of the cesium vapor cell is carried out accurately by using the Beer′s law and then the accurate values of the optical thickness of the cesium atom vapor are obtained finally. Theoretical analysis and experimental result show that higher temperatures lead to larger optical thickness while higher optical intensities result in smaller optical thickness.