A healthy adult's blood loss at a time does not exceed 10%, that is, it does not exceed 400 ~ 500 ml, which will not affect his health. If the blood loss exceeds 20% at a time, that is, more than 800 ~ 1 000 ml, various physiological activities will be affected; If the blood loss exceeds 30% at a time (about 1 200 ~ 1 500 ml), it will be life-threatening.