A terahertz wave switch based on prism-air-graphene-quartz-Si structure was proposed. The dielectric constant of grapheme was changed by the applied external voltage , which make the terahertz wave reflectivity dramatically was changed. The plasma resonance mechanism was used to control of reflected terahertz wave intensity and realize the function of terahertz wave switch. Firstly, the influence of air gap distance on terahertz wave reflectivity is studied. The results show that when air gap is 20 μm, the minimum value of terahertz wave reflectance is 68.79%, When air gap is 56 μm, the minimum value of terahertz wave reflectance is reduced to 0.04% and the air gap distance reaches the optimum value. Secondly, the influence of graphene chemical potential on terahertz wave reflectivity was determined. The results show that when the chemical potential of graphene increases from 0 eV to 0.2 eV, the reflectivity of terahertz wave increases from zero to 95.89% and changes from zero to total reflection. The numerical results also further show that the proposed structure has enormous potential for terahertz wave switch with the extinction ratio of 33 dB.