Abstract: The distribution of oxygen density is relatively stable in the atmosphere. It changes little with latitude and season. Its absorption bands step across 762 nm which is easy to be obtained by non-cryogenic detectors. No other absorption spectrum of atmospheric constituents add to this band. Accordingly, the single station passive ranging based on O2 absorption characteristics and Beer's law was proposed. The absorption rate near 762 nm and 690 nm was used to calculate distance by baseline fitting. An inherent error term was found in application of Lambert-Beer law. It was defined as Nonlinear Initial Value (NIV). Its innate character is the radiation intensity between the lines caused by limitations of instrument characteristics. It can not be eliminated. The experimental platform was built to calculate the distance. For 113 degrees east longitude, 38 degrees north latitude, different seasons, times and weather conditions, a large number of samples were collected to establish the database. Each sample is a relationship between absorption rate and distance in one set of constraints. Empirical model was gotten through statistical fitting. The Nonlinear Initial Value (NIV) in theoretical model was corrected in real time. The distance inversion accuracy is 2.7%.