Brown blood after menstruation may be a normal physiological phenomenon, or it may be caused by luteal insufficiency, gynecological diseases and other reasons. 1. Normal physiological phenomenon: brown blood after menstruation may be the residual menstrual blood in the vagina and the uterine cavity, which is usually a normal phenomenon, usually after a few days, the brown blood can gradually disappear, without special intervention. 2. Luteal insufficiency: If women have luteal insufficiency, that is, the luteal body atrophy is incomplete, resulting in incomplete withdrawal of hormones, and the endometrium can not be completely shed, resulting in significantly longer menstrual period, which results in always having brown blood after menstruation. 3. Gynecological diseases: such as cervical polyps, uterine fibroids, endometriosis, etc., can lead to brown blood after menstruation, which may also be accompanied by increased leukorrhea, lower abdominal masses and other symptoms. Brown blood after menstruation may also be caused by other reasons, if accompanied by obvious discomfort, it is recommended to go to the hospital as soon as possible, after a clear diagnosis of the cause, the doctor guides the treatment.