The temporal properties of nonlinear absorption of a stilbenzene derivative have been investigated by time-resolved pump-probe techniques with picosecond laser pulses at the wavelength of 532 nm. With the help of an additional nanosecond and picosecond open-aperture Z-scan technique, numerical simulations based on a new five-energy level model are used to interpret the experimental results, and the nonlinear optical parameters of this new compound are determined. The five-energy level model is described by two-photon absorption (TPA) excited from ground-state-induced excited-state absorption (ESA) including singlet ESA and triplet ESA. Under the nanosecond pulse excitation, a TPA excited from the triplet excited state contributes to the nonlinear absorption, and the value of the TPA is found to be 1 order of magnitude larger than those usually found for TPA excited from the ground state.