Abstract: Objective To investigate the risk factors affecting the risk and prognosis of placenta implantation,so as to evaluate the risk of placenta implantation according to these clinical high-risk factors,and to compare the sensitivity and specificity of color Doppler ultrasonography and MRI in the diagnosis of placenta implantation.Methods The clinical data of 332 cases of placenta implantation confirmed by pathological examination,including scar uterus or not,number of pregnancy and delivery,number of uterine cavity surgery,placenta previa or not,number of cesarean section and history of vaginal bleeding in early pregnancy were retrospectively analyzed,and these patients were divided into mild group（n=270） and severe group（n=62）.Logistic regression method was used to analyze the high risk factors of placenta implantation.Meanwhile,the sensitivity and specificity of color Doppler ultrasonography and MRI combined with color Doppler ultrasonography for the diagnosis of placenta implantation were compared.Results There were significant differences in the frequency of cesarean section,placenta previa,uterine cavity surgery,pregnancy and delivery and scarred uterus between the mild group and severe group（P＜0.01）,but there was no significant difference in the history of vaginal bleeding in early pregnancy between the two groups（P＞0.05）.Scar uterus,the number of cesarean section and placenta previa were high risk factors for placenta implantation.The rates of postpartum hemorrhage,intraoperative and postoperative blood transfusion,bladder injury,hysterectomy,premature delivery and neonatal asphyxia in the severe group were significantly higher than those in the mild group（P＜0.01）.The sensitivity and specificity of MRI combined with color Doppler ultrasound in the diagnosis of placental implantation were higher than those of color Doppler ultrasound group（P＜0.05）.Conclusions Scar uterus,frequency of cesarean section and placenta previa are high risk factors affecting the risk of placenta implantation.The detection rate of placenta implantation by color Doppler ultrasonography is high,and it can be combined with MRI if necessary.