Complications of diabetes can cause dementia in elderly patients. Diabetes is a chronic metabolic disease based on elevated blood glucose, and long-term poor blood glucose control can produce various acute and chronic complications, which can also easily complicate dementia. Diabetic patients cause dementia for the following reasons: First, long-term hyperglycemia is likely to aggravate the atherosclerosis of elderly patients, affecting brain blood supply and even cerebral infarction, and in severe cases, large multiple cerebral infarcts occur leading to dementia in patients. Second, diabetic neuropathy, diabetes can complicate the central nervous system, vegetative nerves, cranial nerves, peripheral nerves and other neurological complications, there will be a variety of neurological symptoms, also including dementia. Third, diabetic patients in the process of oral hypoglycemic drugs or insulin treatment, due to irregular diet or unreasonable dose of drugs, untimely review of blood sugar and other reasons, often occur hypoglycemia, hypoglycemia will affect the cognitive function of the brain, long-term hypoglycemia can also lead to brain damage and dementia.