Choledocholithiasis is a common clinical condition, and open choledochotomy is effective, but the procedure is very invasive and has many complications. As a safe and effective method, endoscopic retrograde cholangiopancreatography (ERCP) has obvious advantages in diagnosing common bile duct stones by directly showing the common bile duct, and it can be further treated endoscopically to avoid the traditional open surgery, which is becoming more and more popular in clinical application. Ultrasound is an economical, simple, and non-invasive method for the diagnosis of gallbladder stones, but the correct diagnosis rate of common bile duct stones is low because it is difficult to show the whole picture of the bile duct or the common bile duct is obscured by intestinal gas and contents. CT has a higher diagnostic yield for cholesterol stones, but a lower resolution for bile pigment stones, which are often more common in common bile duct stones, so the correct rate of CT detection is lower. Although there is no significant difference between MRCP and ERCP in the diagnosis of common bile duct stones, stones smaller than 4 mm are still missed and may be confused by the coexistence of inflammatory hypertrophy and stones in the lower part of the common bile duct. ERCP can clearly show the morphology of the bile ducts and can make an instant diagnosis for stones with obvious contrast, and can also detect stones by EST followed by mesh basket exploration for those with obvious bile duct dilatation and small stones easily masked by contrast. ERCP can not only clarify bile duct stones, but also, and more importantly, observe papillary lesions and obtain histological specimens for pathological diagnosis. It can show whether the duct lumen is dilated, compressed, filling defect, stenosis and other changes. Therapeutic value】 ERCP can not only improve the accuracy of diagnosis of common bile duct stones, but also can be combined with EST for treatment. For large stones, a lithotripsy basket can be used to remove the stones before mechanical lithotripsy, and for small stones without stenosis and loose duodenal papilla, a lithotripsy basket can be inserted, and the basket can be stretched over the stones and shaken to drag out the stones, which can cure most patients with extrahepatic bile duct stones.