To study the spectrum characteristics of sky background near-infrared oxygen A-band in passive ranging,using the hyperspectral imaging spectrometer,the spectrum of sky background near-infrared oxygen A-band with different zenith angles were measured;Oxygen absorptivity of sky background spectrum with different zenith angles were calculated according to the principle of the passive ranging.The measurement results show:sky background spectrum have obvious characteristic absorption lines in oxygen A-band,and oxygen absorptivity increases with the increase of the zenith angle,which lays the foundation for suppressing the interference of the background and extracting target spectrum accurately in subsequent passive ranging research.