Abstract: The mid-infrared bandpass filter is widely used as an observation channel in applications such as flight, meteorology and remote sensing. The peak transmission and full width at half maximum (FWHM) are key specifications of the bandpass filter, which depend on the film structure and its design.The midinfrared bandpass filter was successfully prepared using a new method with Ge and ZnS materials on Ge substrate. The selection of materials and the design principles of this method were introduced in detail, the film structure is also given. By using ZZSX-1100 device, this kind of filter was deposited with ion beam assisted process. The mea-surement results show that its peak transmission is more than 87% and the FWHM is 70 nm. The filter has good optical spectrum stability and adherence. The film structure is simple and easy to implement.