According to the requirements of sensitivity for gas detection system, based on the characteristics of methane absorption spectrum, combined with the technical experience, the technical indicators of the filter was determined. The "split technology" was used to design the gas filter for the gas filter, which reduced the film stress. The films were deposited by electron beam heating, and the process parameters were optimized according to the test results. The peak transmittance of the filter reached 85.14% at the wavelength of 7.669 μm, and the full of its passband at half maximum is 59 nm, covering the methane gas absorption area. The cut-off depth is OD3 and the narrow-band filter can suppress the background noise well.