The black change of menstrual blood in the last days of a woman’s period may be related to various reasons such as cold, strain, low menstrual blood, obstructed discharge, and suffering from gynecological inflammation. Factors such as cold and fatigue can obstruct pelvic blood circulation, resulting in the endometrial lining peeling off and not excreting in time, presenting as black changes. If there is a tight cervical opening or a change in the position of the uterus that is excessively anterior or posteriorly flexed, the menstrual blood will also appear black due to the low menstrual flow in the last days of menstruation and the longer retention of menstrual blood in the uterine cavity. The color change may also occur if there are diseases such as endometritis or uterine polyps that block the exfoliation of the endometrium. In conclusion, when black menstrual blood changes in the last days of menstruation, women should pay attention to rest, keep warm, eat more hot food, and if necessary, take oral motherwort granules under the guidance of a doctor to promote the timely discharge of black menstrual blood.