<p>Type II endoleak (T2EL), the most common complication after endovascular aortic aneurysm repair (EVAR), remains a leading cause of reintervention due to persistent retrograde flow from patent inferior mesenteric artery (IMA) and lumbar arteries (LAs). The influence of specific anatomical features of these vessels on the hemodynamic environment remains poorly understood. This study evaluated two key anatomical characteristics: branch vessel count and luminal diameter. Eight post-EVAR models were constructed. Computational fluid dynamics (CFD) simulations were performed to quantify key hemodynamic parameters, including flow velocity, pressure, wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT). IMA patency and an increased LA number synergistically primarily altered flow field patterns and shear stress distribution, while larger vessel diameters significantly affected flow rate, WSS directionality, and RRT. Enlarged IMA diameter combined with multiple patent LAs expanded retrograde flow regions and created high-shear-stress environments that inhibited thrombus formation, which may promote T2EL persistence and sac expansion. A risk-stratified embolization strategy was proposed: high-risk patients (IMA ≥ 2.5 mm with ≥ 2 patent LAs) should undergo embolization of IMA and LAs ≥ 2 mm; intermediate-risk (IMA 2.0–2.5 mm or ≤ 1 LA) receive IMA embolization; low-risk patients (IMA &lt; 2.0 mm with ≤ 1 LA) require standard clinical follow-up. This study confirms that an increased number of LAs primarily alters flow field patterns and shear stress distribution within the aneurysm sac, while enlargement of branch vessel diameters elevates perfusion flow rate and pressure. These findings provide a hemodynamic basis for assessing T2EL risk.</p>