Retrograde cholangiopancreatography (ERCP) is a unique and irreplaceable method of pancreaticobiliary duct examination by electronic duodenoscopy. It is an important tool for diagnosing biliary tract diseases.1. Infarct jaundice.2. Biliary stones: Especially for intra- and extra-hepatic biliary stones, ERCP is superior to CT and ultrasound.3. Biliary tract tumors: Especially for non-jaundiced biliary tract tumors, the lesions can be detected early.4. Post-biliary syndrome: ERCP can confirm the diagnosis, such as residual stones and strictures.5. Biliary tract malformation or injury.6. Biliary roundworms. The diagnosis can be confirmed and treated with roundworm extraction, which can have immediate effect.7. Chronic pancreatitis: pancreatic duct stenosis, pancreatic duct stones, combined biliary obstruction, pancreatic cyst, pseudocyst or abscess. The operation process is similar to gastroscopy, but the operation technique is more complicated, and the patient’s feeling is similar to that of gastroscopy, and the patient can go down immediately after the examination, without obvious pain. One hour after the examination and treatment, if there is nothing special, a low-fat semi-liquid diet can be eaten.