Background: The accessory pancreatic duct (APD) is the main drainage duct of the dorsal pancreatic bud in the embryo and varies greatly during development. An APD fistula is a rare and easily neglected complication. In this case report, the first symptom of the patient was postoperative abdominal pain and fever. He was eventually diagnosed with accessory pancreatic fistula combined with duodenal fistula. Such a case has not been reported in the literature. Case Summary: A 66-year-old man was emergently hospitalized for abdominal pain. His preliminary diagnosis was perforation of the digestive tract. He developed fever and abdominal pain after emergency subtotal gastrectomy, followed by changes in the colour of the abdominal drainage fluid. An APD fistula and duodenal stump fistula were confirmed by drainage fluid amylase analysis, contrast fistulography and percutaneous transhepatic cholangial drainage (PTCD). After PTCD, nutritional management and drug treatment, the patient recovered well. Outcome: We found and successfully cured a case of accessory pancreatic duct fistula combined with duodenal stump fistula.