With the rapid development of liver transplantation in China in the past few years, the incidence of post-transplantation comorbidity has decreased year by year, with post-operative biliary complications falling to 3%-20% and mortality to 1-10%, but biliary comorbidity after liver transplantation is still one of the main causes of transplanted liver failure. There are many types of biliary complications and they are associated with postoperative vascular complications, infections and immune rejection, etc. There is no uniform classification. There are two types of complications: those occurring within 30 days after liver transplantation are called early biliary complications; those occurring 30 days or more after liver transplantation are called late biliary complications. And most of the literature classifies them into two main categories according to pathological manifestations: bile leak and biliary obstruction. Bile leaks include anastomotic leaks, hepatic cross-sectional bile leaks, and T-tube associated bile leaks. With the increasing technical refinement of liver transplantation and the use of microsurgical techniques in bile duct anastomosis, the comorbidity of bile leak associated with surgical operation after liver transplantation has been reduced to very low levels. The main bile duct comorbidity that still plagues post-liver transplantation is bile duct obstruction. The causes of bile duct obstruction after liver transplantation are very complex and many factors are involved. Also bile duct comorbidity manifests itself in different clinical types: bile duct anastomotic stricture, bile duct non-anastomotic stricture, bile duct cast syndrome, bile cysts (Biloma aka bile tumors), papillary dysfunction, etc. The main reasons for the occurrence of bile duct anastomotic stricture include: anastomotic technique and local blood supply. There are four main methods for the treatment of anastomotic stricture: 1. Drug therapy: Applicable to patients with mild stricture and very mild impairment of liver function, and the biliary effect can be achieved with drug therapy. 2. Interventional treatment: Most patients with anastomotic stenosis are treated with this method and can achieve definite results. Balloon dilation and placement of stent tubes can be performed via T-tube sinus tract, PTC or ERCP. 3.Surgical treatment: For patients with end-to-end choledochal anastomosis for which interventional treatment is not effective, the anastomotic stricture can be corrected by changing the anastomosis and establishing a bile duct-jejunum anastomosis. Anastomotic stenosis is mostly caused by poor local blood supply to the anastomosis, so the main preventive measures are to shorten the bile ducts with poor blood supply to the liver as much as possible, while retaining the recipient bile ducts with good blood supply to the maximum extent possible, and to reduce the tension of the bile duct anastomosis, but not to make the bile ducts too long after the anastomosis. Microsurgical techniques for bile duct anastomosis are currently advocated. The causes of non-anastomotic bile duct stenosis are complex: whether the donor liver underwent timely and effective intrahepatic bile duct flushing during the first time of cold ischemia, prolonged bile duct secondary thermal ischemia, hepatic artery thrombosis, donor liver excision method, loss of paracolic hepatic artery, prolonged cold and thermal ischemia of the donor liver, ABO blood group incompatibility of the donor recipient, cytomegalovirus infection, chronic rejection reaction, and recurrence of the primary disease (e.g., primary disease of sclerosing cholangitis), etc. There are three main treatment methods for non-anastomotic bile duct stenosis: 1. Oral administration of ursodeoxycholic acid and other drugs that promote bile excretion is often effective in patients with mild stenosis and mild symptoms. It is also helpful for patients with multiple strictures and significant symptoms who are waiting for another liver transplant. 2. Balloon dilation and stent support. Short-term results are good, but good long-term results depend on repeated ERCP interventions, multiple balloon dilation, and replacement of the support tube. Multiple stenoses due to arterial embolism are less effective. 3.Repeat liver transplantation. In cases with hepatic artery embolism, recurrent cholangitis or even liver abscess, and in cases where endoscopic treatment of multiple intrahepatic stenoses is ineffective, retransplantation is the only effective approach. Because of the many causes of intrahepatic bile duct stenosis, prevention of non-anastomotic stenosis of the bile duct should be done in many ways. Most importantly, it is necessary to reduce the donor liver cooling time, to provide timely and effective intrahepatic bile duct flushing at the first time of donor liver excision, to secure the blood supply to the donor bile duct, and to prevent postoperative hepatic artery thrombosis. Bile duct cast syndrome (BCS): This refers to the formation of biliary tree-like casts of necrotic material filling the bile ducts inside and outside the liver after liver transplantation, known as “bile duct casts”, which causes a series of clinical manifestations and may be accompanied by one or more non-anastomotic bile duct epithelial necrosis or stenosis. The causes of BCS include: 1, bile duct blood supply disorder, related to the damage of bile duct blood supply during surgery. 2, physical and chemical factors: bile salts in the bile duct in the ischemic state have a heavy toxic effect on the biliary epithelium, and the mixture of low temperature and UW fluid will aggravate this toxic effect. 3, the quality of liver supply: the shorter the thermal ischemia time and cold preservation time, the lower the incidence of BCS. 4, biliary tract warm ischemia time: resulting in the biliary tract epithelium in the second thermal ischemia, the hepatic artery opening, there is a more serious reperfusion injury. Therefore, the shorter the biliary temperature ischemia time, the more effective it is in preventing BCS. 5, ischemia-reperfusion injury: ischemia-reperfusion injury is also an important cause of acute injury to the biliary epithelium, and the injury is mostly diffuse. 6, surgical skills: with the proficiency of surgical skills and the improvement of understanding of the disease, there is a gradual downward trend. 7, high concentration of contrast agent stimulation. 8, local irritation. 9, dyssecretion of bile components in the new liver: after the new liver resumes blood flow, the secretion of each component (bile salt/phospholipid) in the bile is dysregulated. The higher the bile salt/phospholipid ratio in the bile, the more severe the damage to the bile duct endothelium, and this process is mainly mediated by the toxic effect of high concentrations of bile salt on the biliary epithelium. For BCS, emphasis is placed on prevention, reduction of cold and heat ischemia time of the donor liver, and timely and effective bile duct flushing during donor liver excision and after restoration of blood flow. Biliary cysts: also known as biliary tumors, extrahepatic bile accumulation has become quite rare due to early diagnosis and timely management of bile leaks, however, intrahepatic biliary cysts can occur in areas of intrahepatic segmental obstruction or in areas of severe ischemic destruction of the biliary tree. Secondary infection then causes sepsis and further aggravates the destruction of the biliary system.