Objective: To determine the affecting factors for ultrasound-guided percutaneous catheter drainage (PCD) in treatment of severe acute pancreatitis (SAP) with infected necrosis and the efficacy of its combination with choledochoscopic necrosectomy. Methods: The clinical data of 65 SAP patients complicated with infected pancreatic necrosis undergoing ultrasound-guided PCD as initial treatment during January 2011 to December 2012 were retrospectively analyzed. Results: Thirty-eight patients (58.5%) were cured by PCD only, and in the 27 patients (41.5%) requiring further treatment after PCD, 4 cases were directly converted to open operation, and 23 cases (35.4%) underwent retroperitoneal choledochoscopic necrosectomy, of which 2 cases required an open conversion due to the procedure-related complications. Six patients (9.2%) died after PCD or PCD plus subsequent minimally invasive or open surgical treatment. Results from the comparison of the data between patients who were cured by PCD alone and those requiring further treatment showed that there were no statistically significant differences in the demographic data, severity scores, or other indexes such as white blood cell count, C-reactive protein level and prothrombin consumption test (all P>0.05), and no statistical difference as well in time of the first PCD or the diameter of the catheter drainage tube between them (all P>0.05), but the number of drainage tube placement was greater, drainage time was longer and incidence of complications was lower in the former than those in the latter, with statistical difference (all P<0.05). Conclusion: Number of drainage tube placement, drainage time and puncture-related complications are affecting factors for PCD, and PCD combined with choledochoscopic debridement is a safe and effective minimally invasive treatment for SAP with infected necrosis.