Diabetes mellitus and coronary atherosclerotic heart disease are common chronic diseases at present. Patients with diabetes mellitus of 70%-80% die of cardiovascular system diseases. In addition to epicardial coronary atherosclerosis and myocardial cell damage，diabetic patients also have coronary microvascular dysfunction. Insulin resistance，hyperglycemia，oxidative stress，inflamma－tory factors and free fatty acids are going to decrease the bioavailability of NO，leading to endothelial dysfunction. When endothelial cells are damaged in the body，impaired vasodilation caused by vascular remodeling and hypoxia also occurs，co-working to lead to the coronary microcirculation dysfunction. We reviewed the advance and mechanism of diabetes mellitus in coronary microvascular dysfunction.