Blood pressure value is an important reference of diagnosis and clinical evaluation for the physicians. In addition to being used as the assessment of appropriate medication, many studies have shown that the stability of blood pressure is an important indicator of fatal events such as myocardial infarction, stroke, chronic kidney disease, and organ failure for the patients with hypertension and diabetes. For the patient in surgery, the anesthesiologist must reduce the frequency and degree of hypotension during the operation, shorten the duration of hypotension, and treat the patient according to the physiological state of patient when hypotension occurs. For the patient in intensive care unit (ICU), whether the physician takes immediate treatment for the sensitive events with unstable blood pressure is directly related to the prognosis recovery of patients and the avoidance of acute organ failure.