The normal diameter of the common bile duct is 0.6-0.8 cm. If the diameter of the common bile duct exceeds 0.8 cm on imaging, the diagnosis of dilated common bile duct is usually made. There are many clinical causes of common bile duct dilatation, not all of them are caused by pathological diseases, for example, after gallbladder removal, the common bile duct will compensate for dilatation, which is a normal phenomenon and does not require special stress. However, if there is no such cause, the common bile duct dilatation should be further examined to clarify the cause, and CT, MRI and especially pancreaticobiliary water imaging are commonly used clinically to achieve the best results. Clinically, the pathological causes of common bile duct dilatation mainly include stones, tumors and inflammation, with stones being the most common. Tumors can also cause dilatation of the common bile duct. If painless jaundice occurs in combination with dilatation of the common bile duct, one should be alert to the possibility of bile duct cancer, pancreatic head cancer, and duodenal tumor. For tumorous lesions, radical resection is in principle the most important. If surgical resection is not possible, internal drainage by stent or external drainage by puncture can be considered.