The armchair graphene nanoribbons (AGNRs) can be either semiconducting or metallic, depending on their widths. We investigate the electronic properties of AGNRs under uniaxial strain and electric field. We find that the bulk gap decreases gradually with the increase of the electric field for semiconducting case, but it cannot vanish completely in an appropriate range, which is similar to that of a single uniaxial strain. However, a suitable combination of electric field and uniaxial strain can lead to that the energy gap completely vanishes and reopens. For the metallic case, the bulk gap can display the same opening and closing behavior under an electric field and uniaxial strain. Finally, an interesting quantum phenomenon is obtained by applying a perpendicular magnetic field.
