Diabetic autonomic neuropathy (DAN) is a group of syndromes caused by functional and/or structural impairment of the autonomic nerves, and is a common complication of diabetes mellitus. Diabetic autonomic neuropathy can involve all systems and increase the mortality rate of patients. The pathogenesis of diabetic autonomic neuropathy is still unclear, and there are several theories, the most commonly used being ischemia, hypoxia and metabolic disorders. Diabetes mellitus can be associated with endoneurial microangiopathy, and parasympathetic preganglionic fibers are susceptible to hypoxic damage, which may be one of the reasons why diabetic parasympathetic nerves are vulnerable to damage. In recent years, it is believed that the active polyol pathway and the reduced synthesis of inositol lead to autonomic nerve damage. Other theories include genetic factors and autoimmune damage. (1) Tachycardia: The resting heart rate of diabetic patients increases by an average of about 10 beats compared with normal people, individually up to 130 beats/min. The heart rate slows down less at night and the variability of heart rate decreases, which is related to early vagal nerve damage. In later stages, when both the vagus nerve and sympathetic nerve are involved and the heart is in a completely denervated state, the heart rate does not increase significantly and tends to be fixed at about 80-95 beats/min, and does not respond to stimuli that can change the heart rate under normal circumstances. (2) Postural hypotension: When the patient rises from the prone position, the systolic blood pressure drops > 30 mmHg (1 mmHg = 0. 133 kPa) or the diastolic blood pressure drops > 20 mmHg, especially the diastolic blood pressure drops significantly, or even cannot be measured. Patients often experience dizziness, weakness, palpitations, sweating, visual disturbances, fainting or shock, mainly due to damage to the efferent nerves in the blood pressure regulating reflex arc. (3) Painless myocardial infarction: Myocardial infarction in diabetic patients is often painless or associated with only mild precordial pain, which may be due to interruption of pain transmission due to involvement of myocardial sensory afferent nerves that reduce sensitivity to local myocardial ischemia. (4) Sudden cardiac death: Diabetic patients occasionally suffer from severe cardiac rhythm disturbances (e.g., ventricular fibrillation, flutter) or cardiogenic shock, or even sudden death, due to various stresses. Diabetic autonomic neuropathy can affect the entire digestive tract, mainly due to reduced smooth muscle contraction or low muscle tone. Abnormal esophageal dynamics cause burning sensation, retrosternal discomfort, dysphagia and delayed gastric emptying, which is called “diabetic gastroparesis”. The gallbladder is enlarged and has poor contractile function, but is usually asymptomatic. Neuropathy in the small intestine is characterized by episodes of nocturnal diarrhea that are watery and last from a few hours to a few weeks. Neuropathy of the large intestine is commonly characterized by constipation, and decreased colonic tone may lead to megacolon. 3. Genitourinary system: bladder contraction is weak, asymptomatic in the early stage, but residual urine may increase on examination, urinary retention in the later stage, sometimes filling incontinence, easily combined with urinary tract infection, cystitis, pyelonephritis, etc. Symptoms such as fever, renal colic, urinary urgency, urinary frequency and pain, and sometimes acute renal failure. Recent studies have shown that diabetic autonomic neuropathy plays an important role in the development of diabetic nephropathy. Damage to sympathetic and parasympathetic nerves can impair renal self-defense and cause pathological irreversible changes in renal vasculature, finally causing a decrease in glomerular filtration rate, impaired renal function and corresponding clinical symptoms. Autonomic neuropathy can also lead to retrograde ejaculation, penile erectile failure, and even impotence. In women, menstrual disorders and sexual frigidity may occur. 4, respiratory system Due to chemical, pressure receptor and intrapulmonary receptor lesions and afferent fiber denervation, the afferent impulses are reduced, the respiratory center activity is reduced, resulting in hypoxemia, sometimes with pestle finger, some patients suddenly appear respiratory, cardiac arrest, may be related to the respiratory autonomic neuropathy. 5, other normal people skin temperature from the head to the foot gradually drop, while diabetic patients such temperature gradient is not obvious, or even the opposite. Diabetic patients often have more sweating in the upper body and less or no sweating in the lower body, which is associated with sympathetic nerve damage. Diabetic hyperhidrosis, diabetic hypohidrosis, and localized hyperhidrosis may also be present. In a few patients, the pupils may be narrowed and the light and vergence reflexes may be diminished or absent.