Medium wave infrared devices are developing from monochrome and bicolor to multispectral, metal micro nano structure is the core device to realize the function of medium wave infrared spectroscopy. In order to research the transmission spectrum characteristics of metal micro nano structures in mid infrared band and realize the modulation of transmission spectrum. Based on the principle of Surface Plasmons (SPs), Finite Difference Time Domain method (FDTD) is used to simulate the transmission spectra of thin-film metal micro-nanohole arrays. The influence of the shape and size of the holes, the period of the hole array, the thickness of the metal film and the metal material on the spectral transmittance characteristics of the incident light in the mid-infrared 3.0~5.0μm band is analyzed. By simulating different structures, it is found that the transmittance is mainly determined by the size of the hole. Changing the period of the array can modulate the transmission peak position. The transmittance increases rapidly as the thickness of the metal film decreases, and the metal material Ag is easier to transmit infrared light. Further based on the radius of the circular hole (square hole side length), the array period and the transmission peak position, the least squares method is used to fit the design relations corresponding to different structural models, at the theoretical level, the modulation of the transmission spectrum of the metal micro-nano structure in the 3.0~5.0 μm band is realized, which provides a theoretical basis for the design of multi-channel aperture filter and spectrum detection equipment.