Purpose Placenta accreta is a rare but severe pregnancy complications, and imaging diagnosis is always difficult. This paper aims to analyze the MRI manifestations of placenta accreta, and explore its misdiagnosis reasons. Materials and Methods A retrospective study was carried out on the findings and classification of MRI plain scan and diffusion weighted imaging (DWI) scan of 18 patients with placenta accreta confirmed surgically and pathologically. Results The prenatal MRI scan reported 15 patients of placenta accreta correctly (83.33%), and missed 3 (16.67%) among which 2 were with placenta accreta and the other 1 with placenta increta. The MRI of placenta accreta presented rather thin muscular layer, discontinuous junctional zone, and some unclear boundary of placenta and uterine wall; the signal of the placenta was heterogeneous, and we could see enlarged vessels of extremely low signal on T2 HASTE and high signal on TruFISP sequences, and low signal of thick intraplacental band; moreover, hematoma with high intensity on T1WI and low intensity on T2WI could be seen. DWI demonstrated uneven intensity and dark thicker intraplacenta bands in 2 cases. Conclusion As an important clinical auxiliary tool in diagnosing placenta increta, MRI has high accuracy in the diagnosis of placenta increta and placenta percreta; however, it has rather low accuracy in placenta accreta.