To overcome the shortcomings of the traditional passive ranging technology based on image,such as poor ranging accuracy,low reliability and complex system,a new visual passive ranging method based on re-entrant coaxial optical path is presented.The target image is obtained using double cameras with coaxial optical path.Since there is imaging optical path difference between the cameras,the images are different.In comparison of the image differences,the target range could be reversed.The principle of the ranging method and the ranging model are described.The relationship among parameters in the ranging process is analyzed quantitatively.Meanwhile,the system composition and technical realization scheme are also presented.Also,the principle of the method is verified by the equivalent experiment.The experimental results show that the design scheme is correct and feasible with good robustness.Generally,the ranging error is less than 10％ with good convergence.The opticalpath is designed in a re-entrant mode to reduce the volume and weight of the system.Through the coaxial design,the visual passive range of the targets with any posture can be obtained in real time.The system can be widely used in electro-optical countermeasure and concealed photoelectric detection.