The weight requirement for women to donate blood is: weight greater than or equal to 45kg to be able to donate blood, and weight below 45kg not to be able to donate blood. Because the human body’s blood is proportional to the body weight, the weight of blood accounts for about 7-8% of the body weight. If a girl who is underweight donates blood, the amount of blood in her body is already low. If she donates 200-300ml of blood, the total amount of blood donated may exceed 1/10 of the total amount of blood in her body, and the girl who donates blood may experience pale face, dizziness and weakness, panic and other uncomfortable symptoms after donation. In addition to the weight requirement, women should not donate blood if they are menstruating or breastfeeding, or during pregnancy, because this is a special period that can easily cause obvious effects on the body after blood donation.