Objective:To analyze the clinical characteristics of invasive intervention-related intestinal fistula in patients with acute pancreatitis (AP).Methods:We retrospectively analyzed the clinical data of 177 moderately severe acute pancreatitis (MSAP) or severe acute pancreatitis (SAP) patients who received invasive intervention in Peking Union Medical College Hospital from January 2003 to December 2022. Patients were divided into fistula group and non-fistula group based on the presence or absence of fistula after or during receiving invasive interventions. The age, gender, etiology, systemic inflammatory response syndrome(SIRS), impairment of organ function, revised Atlanta classification, bedside index of severity of acute pancreatitis(BISAP), Balthazar CT classification, extra-pancreatic involvement and secondary infection of local complications, indications, timing and modalities of invasive interventions, length of hospitalization, length of intensive care and outcomes were recorded. The differences on clinical characteristics were compared between the two groups.Results:Intestinal fistulae were found in 21(11.9%) cases during or after invasive intervention, including 8 during or after percutaneous drainage and 13 during or after surgeries. 51 cases received endoscopic drainage or debridement and no intestinal fistula occurred after endoscopic management. Compared to patients without fistula, the median age was younger in the fistula group (36 vs 45 years, P=0.014), and the occurrence of SIRS (95.2% vs 59.6%, P=0.001), extra-pancreatic invasion (100.0% vs 67.3%, P=0.002), and secondary infection (71.4% vs 36.5%, P=0.002) were higher. Patients with fistula had a longer median length of hospitalization (71 vs 40 days, P=0.016) and intensive care (8 vs 0 days, P=0.002). All patients in the fistula group had peri-pancreatic, abdominal and retroperitoneal involvement seen on imaging or intraoperatively. The intestinal fistulae mainly occurred in the colon ( n=13, 61.9%) and the duodenum ( n=6, 28.6%). The confirmed diagnosis of fistulae was based on transfistula imaging ( n=11) or digestive tract imaging ( n=5). Among 13 cases with colonic fistulae, nonsurgical treatment was preferred in 9 cases, and surgeries of fistula repairmen or proximal ostomy were preferred in 4 cases. Among 8 cases with non-colonic fistulae, nonsurgical treatment was preferred in 7 cases, and only 1 case repaired the fistula immediately during the intraoperative detection. Conclusions:Intestinal fistula is an important complication of severe AP, and it is closely associated with invasive interventions. Improved invasive intervention strategies may help prevent intestinal fistula formation; timely and effective management of intestinal fistula may help avoid complications and shorten hospitalization.