Objective　To provide anatomic basis for the onset of acute pancreatitis by explore morphologic features of pancreaticobiliary junction.　Methods　MR cholangiopancreatography (MRCP) of 83 patients with acute pancreatitis (acute pancreatitis group, AP group) were analyzed retrospectively, and their pancreaticobiliary junctions were measured and compared. PRCP of other 139 patients with non-acute pancreatitis was analyzed in the same way as control (control group).　Results　For acute pancreatitis group, the length of common channel was significantly longer than that in control group (P＜0.01), and the angle between common bile duct(CBD) and pancreatic duct in the former was significantly larger than that of the latter (P＜0.01). However, there was no significant difference between the diameters of common bile duct or pancreatic duct in two groups (P＞0.05).　Conclusions　Pancreaticobiliay junction plays a significant role at the onset of acute pancreatitis，meanwhile，long common channel and large angle of pancreaticobiliay ducts are important factors causing acute pancreatitis.