Diabetes mellitus is a systemic disease, poor blood sugar control will produce a variety of acute and chronic complications, but also cause dementia. Diabetes causes Alzheimer’s disease for the following reasons: a. Atherosclerosis, diabetes can accelerate the generation and development of atherosclerosis, affecting the blood supply of cerebral arteries, and even the formation of cerebral infarction, repeated, multiple cerebral infarctions are likely to lead to patients with Alzheimer’s disease. Second, neuropathy, poor glycemic control of diabetes can easily cause a variety of neurological complications, affecting the cognitive function of the brain, leading to Alzheimer’s disease. Third, hypoglycemia, receive oral hypoglycemic drugs or insulin treatment of diabetic patients, when the diet is not regular or the dose of drugs is too large easy to occur hypoglycemia, severe hypoglycemic coma will occur. Hypoglycemia will affect the cognitive function of the brain, and even lead to irreversible brain damage, causing Alzheimer’s disease. Fourth, diabetes combined with other metabolic abnormalities, abnormal hormone levels, such as abnormal insulin levels, increased oxidative stress reaction products, aldose reductase abnormalities, etc., can affect the progress of Alzheimer’s disease.