There are several reasons for the dark color of menstruation: 1. The uterus is in an abnormal position so that menstrual blood cannot be discharged smoothly outside the uterine cavity and then stagnates within the cavity. This turns into stale bleeding when it flows out, so the color will be black. It is recommended that if the uterus is in a retroflexed and retroverted position, resting on your back when you have your period and changing the position of the uterus will improve the dark color of the menstrual bleeding by making it flow smoothly. In addition, if the uterus is in a forward-flexed and forward-tilted position, you can lie flat on the bed and gently press on the pubic symphysis with your hand, which will also improve this situation of dark menstrual blood; 2. The reason in the clinic is because of inflammation of the pelvis and inflammation of the endometrium, which may lead to dark menstrual blood; 3. The lesion of the endometrium of the uterus itself may also appear in this situation, so it is necessary to do gynecological examination and do B ultrasound examination, and then in the clinical to give treatment.