Essential hypertension (EH) is a disease characterized by systematic blood pressure increasing. As a systematic disease, EH can impair not one but many target organs, such as heart, brain, kidney and so on.In the last two decades, the significant correlation between autonomic neuropathy (ANP)and cardiac mortality, especial sudden cardiac death was recognized, Early checking and prediting risk was paid.more attention to autonomic neuropaphy patients in EH. HRV is a non -hurt index in evaluating ANP activity....