Objective To investigate the factors that related to acute biliary pancreatitis including size and the location of the common bile duct stone. Methods Clinical data from 3497 patients with common bile duct stone admitted to the hospital between Jan. 2002 and Dec. 2008 were retrospective analyzed. All patients were grouped according to the size and the location of the bile duct stones. The incidence of acute pancreatitis was compared among groups. Results In patients with common bile duct stone accompanying the acute pancreatitis,common symptoms were fever, bellyache and jaundice, as well as elevated serum amylase. There was a negative correlation between size of the common bile duct stone and the severity of acute hiliary pancreatitis, which was easily induced by the stone in the Vater's ampullar or distal common bile duct. Conclusion Early endoscopic treatment should be carried out in patients with microlith located in the Vater's ampullar or distal common bile duct in order to prevent the acute biliary pancreatitis.