The dynamical TPA cross section as well as optical limiting of BDMAS molecular media for the nanosecond and femtosecond laser pulses is studied.This molecular medium can be described by a cascade three-level model in the visible light regime.Our numerical results show that BDMAS molecular medium exhibits a strong optical limiting behavior.The saturation two-photon absorption in the femtosecond time domain can be observed,and materials with larger nonlinear absorption cross section would be much easier to be saturated.Due to the contribution of the two-step TPA,the dynamical TPA cross section of BDMAS for nanosecond pulses is about three orders of magnitude larger than the one for femtosecond pulses.