This study quantitatively evaluated the effect of chloride (Cl⁻) on the radical distribution and micropollutant degradation in the UV/peroxydisulfate AOP using both experimental and modeling approaches. Results showed that SO₄^•− was significantly scavenged by Cl⁻ at environmentally relevant concentrations (1–5000 mg/L). With increasing Cl⁻ concentrations from 1 to 5000 mg/L, Cl⁻ transformed SO₄^•− to HO^• and then to Cl₂^•−. The critical role of Cl₂^•− as a precursor of HO^• in the radical transformation was highlighted. The inhibitory effects of bicarbonate and dissolved organic matter (DOM) on micropollutant degradation was more significant in the presence of Cl⁻ than that in the absence of Cl⁻, mainly due to the consumption of Cl₂^•− by bicarbonate and DOM. Using the model-predicted radical concentrations in the UV/peroxydisulfate process in the presence of different concentrations of Cl⁻, the degradation rate constants of 34 micropollutants and the contributions of each radical to the degradation were predicted and compared. The findings improved the fundamental understanding of the Cl⁻ effect on radical transformation and micropollutant degradation in the SO₄^•−-based AOPs. The model enables to foresee whether a SO₄^•−-based AOP is effective for the degradation of a certain micropollutant in the water with known concentrations of Cl⁻.