We theoretically simulate one-photon and two-photon absorption spectra for monolayer and bilayer graphene employing the second-order perturbation theory of the electron-photon interaction. The tight-binding model is used to describe the band structure of graphene. The results show that one-photon absorption coefficient of monolayer graphene is a constant about 6.8×107 m-1, demonstrating that the absorptivity of incident light in monolayer graphene approximates to 2.3%. The one-photon absorption coefficient of bilayer graphene changes sectionally with the wavelength and is greater than that of monolayer graphene. The two-photon absorption coefficient of monolayer graphene is proportional to λ4. The two-photon absorption coefficient of bilayer graphene exhibits a giant resonance absorption peak in the infrared (～ 3100 nm) region. Our results will provide theoretical guidance for the application of graphene in the research field of optoelectronic devices.