Menstrual blood is black, may be caused by the following reasons: 1, qi stagnation and blood stasis, if you look carefully you can find that often women will have early or delayed menstruation, menstrual volume is sometimes more, sometimes less, the color will also be darker, during the menstruation will also appear blood clots, breast pain, small stomach swelling pain, etc., most of them are caused by qi stagnation and blood stasis; 2, When women suffer from deficiency of Qi and blood, the dark color of menstrual blood may be caused by long disorders of the menstrual cycle, especially dizziness or lack of energy, pallor, and lack of blood in the face, all of which are due to deficiency of Qi and blood, that is, anemia; 3. It is also the most common cause of black menstrual blood during menstruation. Patients may also experience irregular menstrual cycles, soreness and weakness of the waist and knees, dizziness, tinnitus, and heel pain.