This study aims to explore the effects of different surgical strategies on the “bird-beak” phenomenon during thoracic endovascular aortic repair (TEVAR), so as to provide a theoretical basis for clinical intervention optimization. Three finite element aortic arch models with arch apex angles of 45°, 55°, and 65° were established via finite element simulation. Two stent implantation regions and three gradient stent oversizing ratios of 10%, 20%, and 30% were configured. The bird-beak angle, stent contact area, and vascular wall von Mises stress were quantitatively analyzed to compare the mechanical performance of stent implantation under different parameter combinations. Our results revealed a negative correlation between aortic arch angle and the threshold oversizing ratio required for bird-beak elimination. For 45° small angle aortic arches, 30% oversizing was necessary to resolve the bird-beak effect, whereas merely 20% oversizing sufficed for 55° and 65° larger angle arches. Nevertheless, excessive oversizing of 30% induced stent ring kinking and prolapse, reduced stent vessel apposition area, substantially elevated aortic wall stress, and raised the risk of vascular injury. Furthermore, landing zone 2 implantation was associated with a significantly higher risk of bird-beak formation compared with landing zone 3. In conclusion, stents with >20% oversizing are recommended for patients with 45° small angle aortic arches, with close attention paid to preventing stent deformation. For 55° and 65° aortic arches, 20% oversizing is sufficient to mitigate complications related to bird-beak. These findings offer theoretical support for operative planning and complication reduction in clinical TEVAR practice.