Afferent loop syndrome is an uncommon complication of gastroenterostomy reconstruction after gastrectomy and is easily mistaken for simple acute pancreatitis without urgent surgical indication. We report a case of gastric stump carcinoma complicating afferent loop syndrome and perforation who presented to the Emergency Department with acute pancreatitis. The patient had received partial gastrectomy with Billroth-Ⅱ anastomosis 20 years ago for peptic ulcer. The etiologies of afferent loop syndrome, pathogenesis of acute pancreatitis and the problem of gastric stump carcinoma are discussed.