Causes girls to flow black blood for many reasons, black blood is actually stasis blood discharge, blood color black because there is blood stasis in the body, or bleeding stasis in the uterine cavity or vagina inside for a long time, not timely discharged, the oxygen inside the blood depleted, resulting in the color of the blood black, resulting in vaginal flow black blood is common in the following reasons: First, there may be stasis in the body, resulting in menstrual disorders and blood color First, there may be blood stasis in the body, resulting in poor menstrual flow and darkening of blood color. Secondly, it may be due to miscarriage at the beginning of pregnancy, the bleeding is very small and not discharged in time inside the uterine cavity. Thirdly, it may be caused by poor contraction of the uterus after miscarriage or delivery, and the bleeding inside the uterine cavity is not discharged in time. Fourth, other causes may also cause, such as ectopic pregnancy may cause irregular vaginal bleeding, blood color may be black, brown, bright red, etc.. No matter what the cause, girls bleeding black is an abnormal phenomenon, you need to go to the gynecological examination as soon as possible, a clear diagnosis and timely treatment to prevent the condition from worsening.