In this paper, we make an investigation into the reflectance performance of the Si 3 N 4 self-suspended subwavelength grating (SSG) via changing several parameters including the incident wavelength, the grating period, the grating thickness and the grating filling ratio. For TM polarization of incidence, numerical results by the rigorous coupled-wave method reveal that the reflectance spectrum of the Si 3 N 4 SSG has a narrow linewidth (less than 1nm), high peak reflectance (100%), and low side bands (less than 0.5%) simultaneously in the optical telecommunication wavelength region. By using a micro-electromechanical-systems actuator, it is believed that the Si 3 N 4 SSG should serve as tunable optical filters in optical telecommunication systems.