In order to solve the problem of the poor real-time measurement caused by a hyperspectral imaging system in passive ranging based on oxygen A absorption band, a method of multi-spectral non-imaging measurement for the average transmission of oxygen A absorption band is proposed. In this method, the radiation intensity information of targets located in oxygen A absorption band and its left and right band shoulders is collected by three narrow band filters. Experiments are carried out to measure the average transmission of oxygen A absorption band in the external field, and a photomultiplier tube is used as the photoelectric converter. A line-by-line integral model for oxygen A absorption band transmission is built， and the feasibility of the proposed method is verified when we compare the experimental results with the theoretical results. The contrast results show that the measurement error of oxygen A absorption band average transmission is from 0.146% to 1.576% within the range of 100-400 m, which proves the feasibility of the proposed method.