A nanometric bow-tie aperture has a resonant wavelength where its power throughput is maximal. The incident wavelength should coincide with the resonant wavelength in order to improve the power throughput. However, sometimes it is impossible to tune the incident wavelength, so the resonant wavelength should be tuned alternatively. In order to implement this goal, the relative permittivity of the dielectric substrate of the bow-tie aperture was altered. Finite-difference time-domain (FDTD) simulation results demonstrated that the resonant wavelength is tuned from 569.7 nm to 694.1 nm when the relative permittivity is altered from 1.0 to 3.5. The advantage of this method is that the resonant wavelength can be tuned continuously if the relative permittivity can be altered continuously.