The yellowing of menstrual blood may occur at the beginning of menstruation or one or two days before the end of menstruation. Due to the small amount of bleeding and the long stay in the body, it is easily oxidized and diluted with cervical and vaginal secretions. The color of normal menstrual blood is mostly bright red or dark red. If there are infectious diseases of the reproductive organs, endocrine dysfunction, cold stimulation and other conditions that affect the proliferation and secretion of the endometrium, it may also make the menstrual blood discharged smoothly, yellowish menstrual cycle, menstrual volume and odor change. It is necessary to go to the hospital to take blood test for sex hormone level and ultrasound of the uterine appendages to clarify the cause before taking appropriate medication to regulate.