Menstruation is menstruation, and menstruation with black blood can be caused by too little menstrual flow leading to oxidized menstrual blood, declining ovarian function, induced abortion or multiple intrauterine operations. 1. Low menstrual flow. Under normal circumstances, the color of menstrual blood is usually dark red. If the menstrual blood is black, it may be due to the low menstrual flow, which causes the menstrual blood to flow out slowly, and by the time it flows onto the sanitary napkin, the menstrual blood has already accumulated for a certain period of time inside the vagina, and during this period of time, it will be oxidized, and after oxidation, the color of menstrual blood will be blackened. 2. Decline in ovarian function. Ovarian dysfunction can cause a decrease in estrogen levels, which can lead to dark-colored menstrual blood with low bleeding volume and long discharge time. 3. Some women due to previous abortions or multiple intrauterine operations, resulting in endometrial damage and thinning, or even adhesions in the uterine cavity, the menstrual blood is not discharged smoothly, resulting in the discharge of menstrual blood black color. It is recommended to go to the hospital in time for a detailed examination by a doctor to clarify the cause of menstrual blood black color, and not to blindly self-medication, in order to avoid adverse effects.