▎ 摘　　要

We report a graphene-based tunable ultra-narrowband mid-infrared filter which can be tuned from 4.45122 mu m to 4.44675 mu m by tuning the Fermi level from 0.2 eV to 0.6 eV. Furthermore, the reflection bandwidth is less than 0.2 nm and the reflection rate is more than 0.55. The ultra-narrowband filter is designed based on the guided-mode resonance (GMR) effect. The shift of reflection peak is mainly caused by the change of the real part of the graphene's permittivity. This tunable ultra-narrowband mid-infrared filter can be applied in the mid-infrared microscopy.