Transvaginal ultrasound is a type of intracavitary ultrasound, which is a method of ultrasound examination and diagnosis by placing the ultrasound probe directly inside the vagina. China began to apply transvaginal ultrasound in 1986, because it has the advantages of convenience and speed and high image quality over traditional abdominal ultrasound mainly in some aspects of obstetrics and gynecology diagnosis, plus the application of color Doppler in recent years, it has become one of the essential and important means of obstetrics and gynecology examination, but in some aspects of the use also has certain limitations, which are summarized as follows: Advantages: First, the frequency is higher than One is that the frequency is higher than the 3-5 MHZ probe routinely used in the abdomen, and the resolution is significantly enhanced than that of the abdominal probe. The probe is close to the cervix and posterior fornix in the vagina, unlike abdominal ultrasound, where the sound beam has to pass through various layers of the abdominal wall such as the skin layer, fat layer and muscle layer, bladder and intestines, so the pelvic organs are displayed more clearly. Especially for the observation of posterior uterus and the stratification of uterine wall lesions, such as endometrial lesions (polyps, endometrial cancer, myoma), trophoblastic diseases, posterior pelvic masses, monitoring of follicles, early ectopic pregnancy (before breaking), early pregnancy, placenta praevia, etc., the image display is significantly clearer than that of transabdominal ultrasound. The detection of early pregnancy is detected 5-7 days earlier than abdominal ultrasound. Secondly, there is no need to hold urine, which saves time for the patient, and the patient does not suffer from the discomfort of a full bladder. Third, in obese patients, vaginal ultrasonography is more favorable for clear diagnosis because the probe is close to the cervix, the sound beam is less absorbed and there is no significant attenuation, and the image is significantly clearer than that of abdominal ultrasound. Disadvantages: First, the focus area of the vaginal probe is within 10 cm, and the distant area is not clear. Therefore, transvaginal ultrasound can not show the whole picture in cases of mid to late pregnancy, large fibroids, large pelvic tumors and excessive hypertrophy of the uterus, and abdominal ultrasound is needed for diagnosis. Secondly, the vaginal probe needs to be inserted into the vagina for operation, so it is prohibited for virgins and patients with vaginal deformities, and should be used with caution during menstruation and after miscarriage. Before and after vaginal ultrasound, the ultrasound operator should strictly operate aseptically to avoid cross-infection between patients and contact infection between doctors and patients.