The common causes of menstruation after only 1 day include ovulation bleeding, implantation bleeding and other abnormalities, such as endocrine disorders, ovarian hypofunction, thyroid dysfunction, etc., which need to be dealt with after clarifying the cause of the disease.1. Ovulation Bleeding: Due to fluctuations in estrogen levels, the endometrium is shedding, and there will be transient vaginal bleeding, which is not the real menstruation, and is accompanied by a mild feeling of discomfort in the lower abdomen or lumbar soreness. It is recommended to do ovulation test and basal body temperature measurement; 2. Bleeding on implantation: there may be a small amount of vaginal bleeding when the fertilized egg is implanted, accompanied by abdominal pain, which can be easily mistaken for menstruation for one day, and should be examined by blood HCG to determine whether the pregnancy is; 3. Other anomalies: such as endocrine disorders, ovarian hypogonadism, thyroid function abnormalities and so on, which can cause menstrual irregularities, manifested as shortened menstrual cycle, small menstrual flow, and may be accompanied by abdominal pain, pain in the lower abdomen and pain in the back. The symptoms of irregular menstruation include shortened menstrual cycle, small amount of menstruation, which may be accompanied by abdominal pain, dizziness, premenstrual irritability, nervousness, and dreaming, etc. It is feasible to take hormone test and ultrasound to make it clear, and then choose corresponding treatments to keep the mental health of the patient happy and reduce the pressure on the self.