【Abstract】 Objective To retrospectively analyze the diagnosis of MRI in the lower part of common bile duct obstruction and the causes of misdiagnosis and missed diagnosis. Methods 246 patients with low level biliary obstruction confirmed by surgery, endoscopic retrograde cholangiopancreatography (ERCP) or pathology underwent conventional sequences, magnetic resonance cholangiopancreatography (MRCP) and dynamic enhanced scanning. The causes of misdiagnosis and missed diagnosis were analyzed. Results In 177 cases of benign obstruction, MRI diagnostic accuracy rate was 80.8% (143 cases), misdiagnosis rate was 19.2% (34 cases), 27 cases were misdiagnosed as other benign lesions, 3 cases were misdiagnosed as other malignant lesions, 4 cases were missed diagnosis. In 69 cases of malignant obstruction, MRI diagnostic accuracy rate was 75.4% (52 cases), misdiagnosis rate was 24.6% (17 cases), 11 cases were misdiagnosed as other malignant lesions, 5 cases were misdiagnosed as other benign lesions, 1 cases were missed diagnosis. Conclusion The accuracy of MRI in the diagnosis of common bile duct obstruction is high. The malignant group is slightly higher than that in benign group. Small lesions, interference of various factors, error analysis of image features, lack of knowledge of rare cases, ignoring other lesions, lack of typical signs etc are the reasons. Physicians need to sum up experience, combine with clinical data. Some of the results still need to rely on surgery, ERCP or pathological examination.