The design and fabrication of infrared ultra-narrow bandpass filters is presented, which have been employed in the channel No.1 in the infrared atmospheric sounder (IRAS). The filters are fabricated using Te-rich PbTe as the high-index coating material. By choosing suitable deposition rate and substrate temperature, the carrier concentration in the layers of PbTe can be controlled to a lower level in order to obtain the higher transmittance for the filters. The filters have a central wavelength at 14.95 μm and a bandwidth of 0.065 μm. The relative bandwidth is less than 0.5%. The filter has been used in space and worked stably for five years in the data acquisition of weather forecast.