Objective To evaluate the correlation of oxygen saturation of retinal vessels and diabetic retinopathy (DR) stages or HbA1c level in patients with DR. Methods Cross sectional study. A total of 102 patients (102 eyes) with DR and 20 age-matched healthy controls (20 eyes) (normal control group) were enrolled in this study. DR patients were divided into mild and moderate non-proliferative DR (NPDR) group (55 patients), severe NPDR group (26 patients) and proliferative DR (PDR) group (21 patients). DR patients were also divided into 3 groups according to the HbA1c level including HbA1c＞9% (8 patients), HbA1c 7% – 9% (33 patients) and HbA1c＜7% group (61 patients). The oxygen saturation of retinal vessel was measured by spectrophotometric oximetry unit in the retinal vessels with a diameter greater than 60 μm in the area around the optic disc. Results The retinal artery oxygen saturation of patients in severe NPDR group was significantly higher than that in mild to moderate NPDR group and normal control group (F=13.670,P＜0.05). The retinal vein oxygen saturation of patients in PDR group was significantly higher than that in mild to moderate NPDR group and normal control group (F=6.379,P＜0.05). The difference between retinal artery and vein oxygen saturation of patients in severe NPDR group was significantly bigger than that in mild to moderate NPDR group and PDR group (F=5.536,P＜0.05). The retinal artery and vein oxygen saturation in patients of HbA1c＞9% group were significantly higher than that in HbA1c 7% – 9% group and HbA1c＜7% group (F=9.989, 10.208;P＜0.05). The differences between retinal artery and vein oxygen saturation were same between patients in HbA1c＞9%, HbA1c 7%＜9% and HbA1c＜7% group (F=1.836,P＞0.05). Conclusions The retinal artery and vein oxygen saturation in DR patients are related to the DR stages. Severe NPDR patients show the highest retinal artery oxygen saturation as well as biggest difference between retinal artery and vein oxygen saturation. There is also a trend that retinal vein oxygen saturation increases with higher DR stages. In addition, there is a positive correlation between the levels of HbA1c and retinal vessel oxygen saturation.