Cholangitis is one of the main complications of endoscopic retrograde cholangiopancreatography (ERCP). Plastic biliary stent was used to prevent the occurrence of post-ERCP cholangitis, but the stent should be taken out 1-2 weeks after ERCP with endoscope again. 8.5 F plastic stent with proximal flap can discharge self-driven from biliary to the gut, it has the advantage of avoiding pulling stent out with endoscope again. The purpose of this study is to explore 8.5 F plastic stent with proximal flap on preventing post-ERCP cholangitis of ERCP in patients with choledocholithiasis.