To analyze the timing of delivery selection guided by the ultrasonic measurement of placental marginal thickness parameters of pregnant women with placenta previa, and to study its hemostatic effect. Methods: 98 pregnant women with placenta previa were selected and were randomly divided into two groups from January 2021 to January 2022. 50 women in the observation group were guided to terminate pregnancy by ultrasonic monitoring the thickness of placental margin, and 48 women in the control group were guided to terminate pregnancy according to the relief of abdominal pain and distension, and the amount of vaginal bleeding. The maternal and fetal prognosis of the women in the two groups was recorded. The neonates situation in the two groups were evaluated by 5 min Apgar score <7 points. The changes of white blood cell, red blood cell, and blood red egg of the women were compared between the two groups. The correlation between the placental marginal thickness of the pregnant women with placenta previa and their hemorrhage volume was analyzed. Results: The postoperative red blood cells value (3.34±0.26 1012/L) and white blood cells value (16.47±0.94 1012/L) of the women in the observation group were significantly higher than those(3.09±0.28 1012/L and 13.43±1.05 1012/L) of the women in the control group. The rates of preterm birth (16.0%) and maternal fever (2.0%), the hemoglobin change value (20.12±1.01 g/L), and the blood loss (223.2±38.9ml) of the women in the observation group were significantly lower than those (35.4%, 16.7%, 22.54±0.89 g/L, and 335.8±40.2 ml) of the women in the control group. The Apgar score of neonates at 5 min after born (8.4±0.7 points) in the observation group was significantly higher than that (6.9±0.6 points) in the control group (all P＜0.05). The intraoperative blood loss (232.93±18.93ml) of the women with placenta previa margin thickness ≥10 mm was significantly higher than that (208.30±21.92ml) of the women with placenta margin thickness <10 mm, and the thickness of placenta previa margin of the women with placenta previa was positively correlated with their intraoperative blood loss (all P＜0.05). Conclusion: The timing of delivery of the pregnant women with placenta previa guided by the ultrasonic measurement of placental marginal thickness parameters is helpful to alleviate the hemorrhage during operation and improve the prognosis of the pregnant women and the newborns.