Experimental program is designed to analyze the influence of background radiation on the accuracy of passive ranging based on oxygen spectral absorption; an acousto-optic tunable hyper spectral imaging spectrometer is used as the measuring device and a halogen light as the target. Firstly, the basic principles and experimental program of passive ranging technology based on oxygen absorption are introduced; then the halogen light spectral distribution at different distances during the night is collected using the acousto-optic tunable hyper spectral imaging spectrometer. Oxygen absorption rate is calculated and the relationship model between the oxygen absorption rate and the path is established according to the principle of oxygen spectrum absorption passive ranging. Then the oxygen absorption rate of the target is collected and calculated at the distance of 2360 m for different time. The measuring ranges during the day are solved by the model and the errors are analyzed, the influence of background radiation on the passive ranging is gained finally. Results show that according to the model, the maximum ranging error is 6.74% during the daytime, and the error becomes smaller with the elevation angle of the sun becoming smaller and the background darker. The results give 1.10% ranging error during the nighttime.