In this study, a terahertz amplitude modulator based on metasurface/ion-gel/graphene hybrid structure was designed and fabricated. The modulation performance of the device was simulated and experimentally demonstrated. This device uses the ion-gel medium embedded between graphene and metasurface as the electrolyte, and the graphene as the active material. The enhancement of the interaction between terahertz wave and graphene is realized on the metasurface. Further, an external bias voltage was used to tune the electrical conductivity of graphene for actively controlling the terahertz waves. The results indicate that the device can achieve a modulation depth of up to 73% at the resonant frequency with a relatively small bias voltage. Moreover, the resonant frequency remains almost constant in the modulation process. Thus, the proposed device provides one novel tool in the large terahertz amplitude modulation under low voltages.