Realization of passive ranging based on infrared radiation and atmospheric attenuation characteristics is closely related to gas band selection. Oxygen A absorption band has a unique spectral structure. For rocket plume and high temperature radiation, the band is the best inversion channel of distance. Through the in-depth research of line-by-line radiative transfer model (LBLTRM), Oxygen A band standard spectrum calculation software is designed. Making use of the out-of-band data, band average transmittance in different distances is obtained by polynomial fitting, and then the corresponding distance is received. Putting the ABB lamp as the light source, collecting the corresponding spectrum in different distances and making the fitting calculation, through the comparison of fitting results of the measured datas and theoretical calculation results, the error is within 0.5% and is in the permissible range.