Black discharge after menstruation is commonly caused by residual menstrual blood in the uterine cavity or gynecological inflammation. 1. Residual menstrual blood in the uterine cavity: After menstruation, there may be residual menstrual blood in the uterine cavity, which will be oxidized and cause black discharge, which is a normal physiological phenomenon, and it will disappear on its own in about 1~2 days and will not cause any adverse effects. 2. Gynecological inflammation: for example, vaginitis or endometritis, due to the presence of inflammatory substances, will lead to black discharge after menstruation, and may also be accompanied by vaginal itching, abdominal distension and other symptoms. When the black discharge is accompanied by vaginal itching and other uncomfortable symptoms, it is recommended to go to the gynecology department of the hospital for routine testing of the leukorrhea, a clear diagnosis, and then targeted treatment.