Hyperuricemia is a prevalent metabolic disorder, and xanthine oxidase (XO) inhibition remains a primary strategy for its management. In this study, a novel food-derived XO inhibitory octapeptide, SRGQIEEL, was identified from yellow field pea (Pisum sativum L.) protein hydrolysates through activity-guided purification. Among six proteases tested, the Alcalase hydrolysate showed the strongest XO inhibitory activity, with an IC50 value of 0.60 mg/mL. Sequential ultrafiltration and RP-HPLC purification, followed by nanoUHPLC-ESI-Q-TOF MS, identified SRGQIEEL as the major active peptide. The synthesized peptide exhibited an IC50 of 193.34 μM and showed non-competitive inhibition kinetics, with a Ki value of 137.29 μM. Multi-site molecular docking across four cofactor-associated regions in two bovine XO structures consistently indicated that SRGQIEEL preferentially associated with the FAD domain rather than the conventional Mo-pt active site. Subsequent 100 ns molecular dynamics simulations and MM-PBSA calculations supported favorable association with the FAD region. Dynamic tunnel analysis further revealed that the FAD access tunnel remained predominantly too narrow to accommodate the peptide, supporting a tunnel-occlusion-like mechanism. Collectively, these findings suggest that SRGQIEEL inhibits XO not by entering a deeply buried active site, but by associating near the FAD-domain tunnel entrance and potentially perturbing electron transfer. This study highlights the value of dynamic tunnel accessibility analysis for investigating food-derived peptide inhibition of XO.