Abstract: Objective：To compare the value of three-dimensional ultrasound and MRI in the early prediction of cesarean scar pregnancy（CSP） after cesarean section.Methods：The clinical data of 43 patients with suspected CSP admitted to our hospital from February 2018 to February 2019 were retrospectively analyzed. The early diagnosis of uterine CSP after cesarean section was analyzed by three-dimensional ultrasound and MRI.Results：Postoperative pathology confirmed 39 patients with uterine scar. 30 cases were correctly diagnosed by three-dimensional ultrasound， and 4 cases were false positive. The diagnostic sensitivity was 85.71%， the specificity was 50.00%， the positive predictive value was 88.24%， the negative predictive value was 44.44%， and the accuracy rate was 76.92%.The diagnostic results of MRI were 29 cases， 5 cases， 93.54%， 58.33%， 85.29%， 77.79%， and 74.36% respectively， and the difference was not statistically significant (P>0.05). MRI is superior to three-dimensional ultrasound in examining the number of yolk sac， the number of embryos， and the number of original cardiac pulsations. The three-dimensional ultrasound is better than MRI in examining the intra-pregnancy sac bleeding， local scar infiltration， and hematocele in uterine cavity. The differences were statistically significant (P<0.05). Conclusion： Three-dimensional ultrasound and MRI have higher accuracy in diagnosing uterine scar. MRI shows that internal hemorrhage in gestational sac， hematocele in uterine cavity， and the relationship between gestational sac and incision and surrounding tissues are superior to three-dimensional ultrasound， while three-dimensional ultrasound is superior to MRI in detecting yolk sac， embryo bud and primitive heart tube pulsation， etc. The combination of the two has important value in diagnosing and treating uterine scar.