In order to measure retinal oxygen saturation, a dual-wavelength retinal oximeter based on commercial fundus camera was designed. The system made the retinal image of the commercial fundus camera second imaging, and simultaneously collected dual-wavelength images that respectively represented the same absorption coefficient wavelength images and the different one of oxygenated hemoglobin and de-oxygenated hemoglobin. The retinal oxygen saturation was finally measured after image registration, vessel segmentation and calculation of optic density ratio of the two images. The means oxygen saturation of artery and venules in health human for repeated measurements were 92.85% and 56.75%, respectively. The mean standard deviation was 2.41% for arterioles and 3.63% for venules.The data demonstrate that the system is reliable and reproducible. The system can obtain retinal structural imaging, which provides a useful tool for research of life sciences and diagnosis of retinal-related diseases.