A metal-dielectric-metal grating infrared emission/absorption structure is designed for narrow-band infrared emitters or detectors in application of spectral imaging sensors and biomaterial absorption spectroscopy. By using finite difference time domain (FDTD) method, reflection spectrum of the one dimensional Ag/Si3N4/Ag grating structure is simulated. The results show that very narrow mid-infrared emission/absorption peak is generated in this structure for both TE and TM polarizations and emittance above 98% at the central frequencies can be achieved for both polarizations over a broad emission direction. The origin of this performance is believed to come from the excitation of waveguide mode and surface plasmon mode in this structure.