Whether the high pressure is lower than 100mmHg is normal and dangerous, need to clarify the specific low how much, if between 90 ~ 100mmHg is normal, no danger; if lower than 90mmHg belongs to the low blood pressure, the lower the value of the risk is greater. High pressure usually refers to systolic blood pressure. According to the standard of blood pressure, the normal value of systolic blood pressure should be between 90~139mmHg, between 90~119mmHg belongs to normal blood pressure, between 120~139mmHg belongs to the normal high value of blood pressure. Therefore, if the high pressure is lower than 100mmHg, but greater than 90mmHg, it is normal blood pressure, and there is no danger from the point of view of blood pressure alone. However, if the high pressure is lower than 90mmHg, it suggests that hypotension may exist. Multiple measurements should be taken and evaluated in conjunction with the diastolic blood pressure. If hypotension does exist, the lower the blood pressure value, the more dangerous it is. Low blood pressure generally has certain effects on the human body, such as can lead to insufficient blood supply to the whole body tissues, affecting the function of the brain, heart, kidneys and other organs, often can appear weakness, dizziness, chest tightness, chest pain, etc., and in serious cases, can lead to fainting. Some accidents induced by dizziness can also cause secondary trauma and other injuries. In summary, daily blood pressure measurement can be strengthened, such as long-term systolic blood pressure below 90mmHg, diastolic blood pressure below 60mmHg, should pay attention to timely medical care, clarify the cause and regulate blood pressure.