Passive ranging has received much attention because of its concealment. The distance between sensor and the object is measured by the infrared radiation attenuation in atmosphere. A mono-station single-band ranging method based on spectra transmission characteristics of oxygen is developed. The concept of light of sight (LOS) is introduced. The ray tracing model is built. With the method of discrete transfer and the discretization of physical properties distribution field of oxygen, the radiation strength in oxygen band of the target is calculated by the LOS along the seeker detectors. The radiation strengths in resonant frequency band and non-resonant frequency band are analyzed. The distance is achieved by their relation. High-resolution spectrometer is adopted to build experiment platform. Real-time dynamic ranging can be implemented by field calibration. The present experimental range is 75-200 m. The maximal relative error is 7.56%.