Whether the duration of menstruation for 3 days is normal or not needs to be determined on a case-by-case basis, as follows: 1. Normal: If the usual menstrual period is 3 days and there are no other uncomfortable symptoms and normal menstrual volume, i.e., using 10 sanitary napkins/packet each time, and each piece of blood is more than 50%, it is normal; 2. Abnormal: 1. The previous menstrual period was 3 days, but the presence of abdominal pain, darker blood color or reduced blood volume is abnormal. 2. If the usual menstrual period was 5-6 days, but now it becomes 3 days and the blood volume is reduced and black, it is usually due to the presence of pelvic inflammatory disease, tubal inflammation or impaired ovarian function. 3. Some women belong to ovulatory bleeding, which lasts 2-3 days and is similar to menstrual bleeding.