On the basis of the development of the model of transient state spectral absorption coefficient and ultrafast carrier dynamics, a theoretical model is established, which can describe the transient bleaching mechanism induced by femtosecond laser, so as to investigate the characteristics of the transient bleaching of direct bandgap semiconductor. The results indicate that femtosecond laser can not only induce the corresponding spectral bleaching but bleach the spectrum ranging from the exciting wavelength to the semiconductor′s long wavelength cutoff as well, and the effect becomes more obviously with the increase of laser wavelength and even results in negative absorption phenomena at the bottom of band.