To investigate the effects of irradiation on the degradation of sodium benzoate in aqueous solution and the underlying mechanisms, sodium benzoate solutions at different concentrations (0.5, 1, 3, 5, and 7 mmol•L-1) were subjected to irradiation at doses of 1, 3, 5, 7, and 9 kGy. Sodium benzoate degradation was monitored by gas chromatography (GC), and the degradation kinetics were analyzed. Quantum chemical calculations were performed to elucidate the irradiation-induced degradation mechanism. In addition, the effects of irradiation on the antibacterial capacity of sodium benzoate were evaluated experimentally using pathogenic bacteria. At the tested concentrations, the degradation rate of sodium benzoate increased with increasing irradiation dose, reaching nearly 100% at lower concentrations. Sodium benzoate degradation under irradiation followed first-order kinetics. Trace amounts of phenol were detected after irradiation of high-concentration sodium benzoate solutions. Mechanistic analysis indicated that sodium benzoate reacted with hydroxyl radicals under irradiation to form degradation products, with a freeenergy activation barrier of 11.3 kcal•mol-1 and an exothermic energy release of 17.2 kcal•mol-1. The antibacterial capacity of sodium benzoate decreased progressively with increasing irradiation dose. Overall, both irradiation dose and initial concentration significantly influenced the degradation rate of sodium benzoate, the formation of phenol, and antimicrobial activity. To maintain effectiveness, sodium benzoate should be used at an appropriate concentration within the permissible limit (6.94 mmol•L-1), and the irradiation dose should be selected according to the applied concentration. This study provides a theoretical basis for understanding the behavior and mechanisms of sodium benzoate degradation under irradiation.