Black blood appears during menstruation, if it is a few days before menstruation may be due to low vaginal bleeding in early menstruation, long retention time, and the influence of acid-base environment, which is a normal physiological phenomenon and can be relieved by itself after the increase of menstruation. But if the menstruation has been black blood may be due to the following types of menstruation: 1, the patient greedy cold, cold blood cold, menstrual blood clotting, menstrual black phenomenon; 2, the patient’s physique is qi stagnation blood stasis type, menstrual blood elimination may not be black; 3, the patient plain kidney deficiency, congenital endowment deficiency or acquired careless regimen may also lead to black menstruation; 4, excessive dieting leads to the body protein The lack of protein and fat in the body can affect the synthesis of hormones in the body and lead to black menstruation; 5. Patients with uterine cavity adhesions caused by uterine surgery can lead to poor elimination of menstruation or even amenorrhea, and affect the color of menstruation.