By using the self-suspended subwavelength grating (SSG), a new kind of tunable optical filter is proposed. The reflectance performance of the SSG versus the tuning grating period is analysed in detail based on rigorous electromagnetic theory and the coupled wave method. For the SSG fabricated with SiO2 material in the case of TM polarization, numerical results reveal that the designed optical filter simultaneously possesses a narrow linewidth (less than 1 nm), high reflectance (higher than 99.9%), and low side bands (lower than 0.5% ). In addition, through a micro-electromechanical systems actuator, the narrow-linewidth filter has a tunable range of about 200 nm in the optical telecommunication wavelength region. Therefore, it is highly expected to have practical applications in optical telecommunication systems or wavelength-division multiplexing systems.