The absorption induced by intersubband transition in semiconductor superlattice was studied.Numerical illustrations of the optical absorption in a GaAs/Al_xGa_1－xAs superlattice were given. The optical absorption coefficient as a function of the incident optical frequency,the optical intensity,the temperature and the structure parameters of superlattices(The width of quantum well,the barrier width and the composition percent of Al) were obtained. The simulation results showed that the absorption spectra of superlttice appeared as asymmetric absorption band. The optical intensity only changed the magnitude of absorption coefficient. The structure parameters of superlattice could change the width of absorption spectra and the resonant photon energy. The wider the well or barrier were,the narrower the absorption band became the smaller the center absorption band,the bigger was the absorption coefficients,and the absorption peak red shifted. The absorption band became narrow and the absorption coefficients increased when the composition percent of Al increased.