If the dilatation of common bile duct is greater than 1cm, further examination may be needed to determine if the dilatation is caused by other diseases. Clinically, dilatation of the common bile duct is mainly seen in choledocholithiasis, malignant tumor of the lower part of the common bile duct, malignant tumor of the head of the pancreas and malignant tumor of the jugular abdomen of the duodenum, and CT or magnetic resonance examination can be improved to exclude whether the dilatation of the common bile duct is caused by these diseases. If these diseases are excluded, a dilated common bile duct larger than 1 cm is not relevant.