Objective: To investigate the ultrasonography and low-field MRI in the prenatal diagnosis of placenta increta. Methods: Retrospective analyse 58 women diagnosed with placenta increta from January 2006 to January 2014 at affiliated Hospital of Wenzhou Medical University, all patients were confirmed by clinical and/or pathology after postpartum, and all were given Doppler ultrasound and MRI to monitor placental growth situation. The sensitivity and accuracy of Doppler ultrasonography and MRI for prenatal diagnosis of placenta increta were analysed. Results: In 58 patients with placenta increta, Doppler ultrasound diagnosis of 31 cases, coincidence rate was 53.4%(31/58), MRI diagnosis of 39 cases, coincidence rate was 67.2%(39/58). Two kinds of diagnostic methods have no statistical significance(P＞0.05). Combined diagnosis coincidence rate was 82.8%(48/58). Three kinds of diagnostic methods have statistical significance(P＜0.05). Patients with placenta are located in the back wall, Doppler ultrasound diagnosis of 14 cases, coincidence rate was 43.8%(14/32), MRI diagnosis coincidence rate was 57.1%(23/32). Two kinds of diagnostic methods have statistical significance(P＜0.05). When the signs of thickening of the placenta, disappear of placenta back gap and so on were detected, the diagnosis coincidence rate was 48.3%(28/58), single sign was difficult to determine whether it was placenta implantation. When there were direct signs showed on MRI, the diagnosis coincidence rate was 53.4%(31/58), while the indirect signs of the diagnosis coincidence rate was only 13.8%(8/58), the difference was statistically significant(P＜0.05). Conclusion: When placenta locates in the uterus back wall, MRI is more accurate than the Doppler ultrasound examination it can be used as an important supplement of the Doppler ultrasound examination. When many signs of placenta increta appeared on ultrasonography and direct signs appeared on MRI, it should be considered of placenta increta.