Abstract: Objective To analyze the risk factors of occurrence of complications after fenestrated or branched endovascular aortic repair (F/B-EVAR) for complex thoracoabdominal aortic diseases. Methods Clinical materials of 147 patients with F/B-EVAR for thoracoabdominal aortic diseases in the Department of Vascular Surgery of Drum Tower Hospital Affiliated to Medical College of Nanjing University from 2021 to 2023 were retrospectively analyzed. Multivariate correlation analysis was used to explore the risk factors for postoperative complications during the mid-term follow-up. Results There were 13 postoperative deaths, with a mortality rate of 8.8%; 52 patients experienced overall surgery-related complications, with an incidence rate of 35.4%; 31 patients had postoperative endoleaks, with an endoleak rate of 21.1%; 14 patients had branch stent-related endoleaks, involving 14 branches; and 4 patients had branch occlusion, involving 5 branches. The re-intervention rate in this study was 20.4% (30/147), with 20 cases (13.6%) of postoperative renal insufficiency and 1 case of postoperative paraplegia due to spinal cord ischemia, as well as 1 case of postoperative stent infection. Risk factor analysis for postoperative mortality, overall complications, endoleaks, and postoperative renal failure was conducted, and the risk factors for overall complications included preoperative renal insufficiency, aortic disease, aortic tortuosity angle >60 °, and average number of branch reconstructions. The independent influencing factors for postoperative endoleaks included gender, age, history of renal insufficiency, history of thoracic endovascular aortic repair (TEVAR), aortic tortuosity angle >60°, and true lumen diameter in thoracoabdominal aortic dissection (TAAD). The independent influencing factor for postoperative renal failure was preoperative renal insufficiency. Conclusion Female, age, thoracoabdominal aortic aneurysm (TAAA), history of renal insufficiency, history of TEVAR, aortic tortuosity angle >60°, and true lumen diameter in TAAD are the influencing factors for postoperative complications in patients with thoracoabdominal aortic diseases, and the possible related factors are TAAA sac diameter and TAAD false lumen diameter.