The patient, Zhou Moumou, female, 17 years old, no history of sexual life, 14 years old, first menstruation, no dysmenorrhea, regular menstrual cycle, no significant prolongation of menstruation, irregular vaginal bleeding with no obvious cause in the past 1+ months, dark red, no clots, no abdominal pain, has been transferred to several municipal hospitals, ultrasound has been done several times, gynecological endocrinology has also been tested, but never clear diagnosis, hemostatic and menstrual regulating drugs have been used a lot, but the effect is not satisfactory. The effect was not satisfactory, so she finally came to our hospital. I saw the 17-year-old girl in the gynecology clinic. After checking the girl’s previous ultrasound results, I found that the girl had a double uterine malformation, and after further detailed examination, combined with my previous experience, I was basically sure that the girl had vaginal diaphragm syndrome type II, and that the persistent vaginal bleeding was due to poor drainage of menstrual blood caused by the accumulation of blood in the post-diaphragmatic cavity. She explained to her mother about her condition and the cause of her vaginal bleeding, and explained that she needed to be hospitalized for a hysteroscopic examination of the vagina to confirm this diagnosis. After explaining the condition to the girl and her mother, they agreed to the surgery and after excluding any contraindications to the surgery, the vaginal diaphragm was successfully removed and the patient recovered well. The cause of vaginal strabismus syndrome, also known as Herlyn-Werner-Wunderlich syndrome (HWWS), is still unclear and may be due to a blind end of the paramedian tube that does not extend down to the genitourinary sinus. Vaginal strabismus is often associated with ipsilateral urogenital developmental abnormalities, most often with bilateral uterine bodies, bilateral cervix and renal agenesis on the side of the strabismus. There are three types of vaginal oblique septum. Type I is a nonporous septum. The uterus is completely isolated from the outside world and from the other side of the uterus, and blood accumulates in the posterior cavity of the septum. Type II is an empty oblique septum. There is a small hole of several millimeters on the septum, and the uterus after the septum is isolated from the other side of the uterus, and the menstrual blood drips out through the small hole, and the drainage is poor. There is a small fistula between the two uterine cervixes or between the posterior cavity of the septum and the opposite uterine cervix. The clinical manifestations of vaginal diaphragm syndrome are young age of onset, normal menstrual cycle, dysmenorrhea in all three types, type I is more severe, usually with pain in the lower abdomen on one side; type II has a small amount of brown vaginal discharge or old blood dripping between menstrual periods, with infection there is purulent discharge with odor; type III has a small amount of blood during prolonged menstruation, infection can also have purulent discharge. Cystic masses can be palpated in the vault or vaginal wall on one side during gynecological examination. The treatment of this disease is relatively simple, and can be cured by surgical excision of the diaphragm after a clear diagnosis, and by ensuring smooth drainage of menstrual blood. In this case, the patient presented only with irregular vaginal bleeding without dysmenorrhea, and the symptoms appeared only 3 years after the onset of menstruation, which is rare, and may be the reason why the patient could not get a clear diagnosis despite repeated visits. The treatment of this patient suggests us to look for multiple causes, and a careful and conscientious physical examination is irreplaceable for the diagnosis of the disease by any modern instrument.