This study presents the design of a metal-insulator-metal curved waveguide filter coupled with an embedded-silver-bar disk cavity, which is based on the transmission and coupling characteristics of surface plasmon polaritons. Herein, the spectral and filtering characteristics of the proposed structure are analyzed via the finite element method. The results indicate that the dual-mode resonance effect is achieved because the silver bars embedded into the disk cavity destroy the structural symmetry. In addition, the structure possesses the bilateral coupling effect, which makes the coupling efficiency higher than that for single-sided coupling. There exist two distinct forbidden bands in the transmission spectrum and the good dual-band narrowband filtering function is obtained. Furthermore, a quality factor higher than those of the previously reported filters is achieved. The wavelength of such a filter can be approximately linearly adjusted by varying the radius of disk cavity or the refractive index of the medium in the cavity.