The transmissivity and conductivity of the few-layer graphene with 600 nm CW laser and two substrates are measured and analyzed, based on terahertz time-domain spectroscopy and the Drude model. In this study, the absorption of terahertz signal is obviously enhanced through the graphene on high-resistivity silicon or the absorption of terahertz signal is slightly decreased through the graphene on PET (Polyethylene terephthalate) with the excitation of external laser. At 0.5 THz, the conductivity of the graphene on high-resistivity silicon is increased by 7 times or the conductivity of the graphene on PET is felled to 77%, compared to that without external laser. Meanwhile the experiments verify that the conductance in the few-layer graphene appears as the linear superposition of per layer among the THz waveband.