Abstract: A novel subwavelength surface plasmon polaritons optical filter based on metal-dielectric-metal (MDM) waveguide with the semicircular cavity is proposed and investigated. Temporal coupled mode theory and the finite difference time domain method (FDTD) are utilized to analyze the structure and get the transmission response. The filter characteristic and the dependence of the resonant wavelength on geometric parameters of the structure are also discussed in this paper, and a type of double cavities structure is designed in order to realize higher transmission contrast.