Since its introduction in 1968, endoscopic retrograde cholangiopancreatography (ERCP) has become a commonly performed endoscopic procedure, and the first choice in the management of choledocholithiasis. Although as an endoscopic minimally invasive procedure, there are still certain complications of ERCP, cholangitis is one of the main complications. In European and American countries, 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. In China endoscopic nasobiliary drainage is usually adopted to prevent post-ERCP cholangitis. Although nose bile duct was more convenient to pull out without endoscope again, but patients often feel nose pharynx ministry unwell obviously. 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.