According to the hypertension diagnostic criteria, hypertension can be classified as grade I, II, or III, and hypertension grade III is severe hypertension. Hypertension is diagnosed if systolic blood pressure is ≥140 mmHg and/or diastolic blood pressure is ≥90 mmHg when the office blood pressure is measured three times on non-same day without the use of anti-hypertensive drugs. Patients with a previous history of hypertension, who have received regular blood pressure lowering therapy, were diagnosed with hypertension despite a blood pressure <140/90 mmHg. In a population with a continuous normal distribution of blood pressure levels, there is no clear line of demarcation between normotension and elevated blood pressure, and the criteria for hypertension are defined based on clinical and epidemiological data. Normal blood pressure is systolic blood pressure <120 mmHg and diastolic blood pressure <80 mmHg; normal high values systolic blood pressure 120-139 mmHg and diastolic blood pressure 80-89 mmHg. Hypertension is further classified into three levels according to the level of elevated blood pressure. Grade I hypertension (mild) is systolic blood pressure 140~159mmHg and diastolic blood pressure 90~99mmHg; Grade II hypertension (moderate) is systolic blood pressure 160~179mmHg and diastolic blood pressure 100~109mmHg; Grade III hypertension (severe) is systolic blood pressure ≥180mmHg and diastolic blood pressure ≥110mmHg. In summary, it can be seen that hypertension grade III is severe hypertension. Severe hypertension is very dangerous and may induce life-threatening conditions such as cerebral hemorrhage, heart failure and renal failure, and requires medical attention as soon as possible.