The effects of the length of the embedded metal strip and the width of the gap in the metal-insulator-metal waveguide structure on the optical transmission characteristics have been investigated using the finite-difference time-domain method. The result shows that, compared with the single straight waveguide, an obvious transmission peak appears in this structure. Moreover, the Fabry-Perot cavity is generated by the gap between the metal strip and the metal at the top surface of the waveguide when the length of metal strip is relatively large. The high order resonant mode is stimulated, the energy is resonated continuously in the Fabry-Perot cavity, and multiple resonance peaks of attenuation are generated. Meanwhile, a surface plasmon polariton bandpass filter based on embedded double metal strip is proposed. The transmission of this filter can be down to zero except the resonant peak. In addition, the resonant wavelength can be adjusted by changing the various parameters such as the length of the metal strip.