The normal internal diameter of the common bile duct is usually no more than 1 cm. If the widening of the common bile duct is greater than 1 cm, it is considered to be a dilated common bile duct. There are many clinical causes of common bile duct dilatation, including stones in the common bile duct, benign and malignant swelling of the common bile duct, tumors in the head of the pancreas, and tumors in the abdomen of the duodenum, which may lead to dilatation of the common bile duct. There are also some congenital diseases, such as congenital cystic dilatation of the common bile duct, which can also lead to dilatation of the common bile duct. In some patients after cholecystectomy, his common bile duct can also be compensated for the dilation. In some elderly people, geriatric physiological dilatation can also occur. Therefore, the cause of the dilatation of the common bile duct should be clearly identified and treated only after the cause is clearly identified.