To Analyze the prenatal factors and forecast the success rate of vaginal delivery of twin pregnancy. Totally, 114 cases of twin pregnant women who were under the systematic antenatal care and had deliveries in Beijing Obstetrics and Gynecology Hospital from January 2017 to March 2019 were collected. The inclusive criteria were uncomplicated twin pregnancy with head downward position of the first fetus, not monochorioallantoic twin twins, and the willingness for vaginal delivery. Two groups were classified based on their successful vaginal delivery. 96 cases in vaginal delivery group (study group) and 18 cases in the comparison groupwhich were transferred to Caesarean sections during trial delivery. The evaluated prenatal factors included: (1) Fetal factors: the chorionicity of the twin pregnancy, position of the second fetus, fetal weights and the weight difference of two fetuses. (2) Maternal factors:the maternal age, delivery gestational age, parity, body mass index (BMI), reasonability of weight gain during pregnancy, pregnancy complications, such as gestational diabetes mellitus (GDM), hypertensive disorder of pregnancy, and the application of assisted reproductive technology. (3) The technical title of the delivery doctor, modes of labour (spontaneous labor or induced labour and its mode) and the application of labor analgesia, etc. Single-factor logistic analysis and multiple-factor logistic regression were used to do statistical analysis and nomograms were plotted, finally receiver operating characteristic (ROC) curves and standard curves were formed for internal verifications and Youden index were utilized to determine the cut-off values. Five variables:maternal age,complicated GDM, reasonability of weight gain during pregnancy, parity, and the weight of the second fetus is less than the firsthad obvious influence on the success rate of vaginal delivery in twin pregnancy. After quantifying the influence weight, the influence of each factor was as follows:the age of the mother 35 years old: 64; no GDM: 100, no insulin application in GDM: 47, and application of insulin: 0; reasonability of weight gain during pregnancy: 82; parity≥2: 58; and the weight of the second fetus was less than the first: 57. The ROC curve was plotted and the area under the curve (AUC) is 0.856 1, which were able to forecast the success rates well, the maximum value of the Youden index was 0.564 7 and the corresponding score was 168. maternal age, reasonability of weight gain during pregnancy, the complication of GDM, parity, and the weight of the second fetus less than the first are the influential prenatal factors on vaginal delivery of twin pregnancy. After assigning the influence weight of each influencing factor, when the total score reaches 168 the success rate of vaginal delivery is significantly improved.