Carbonate (CO 3 2- /HCO 3 - ) have a significant impact on advanced oxidation processes (AOPs) by consuming reactive free radicals such as HO • to generate CO 3 •- . However, research on the mechanisms and kinetics of CO 3 •- remains limited. This study investigates the degradation mechanism and kinetics of sulfonamide antibiotics (SAs) by CO 3 •- through theoretical calculations. The calculation results revealed that the effect of CO 3 •- on SAs degradation is pH-dependent due to the dissociable sulfonamide group (-SO 2 NH-) of SAs in the common water treatment pH range (3-8). The main reaction type of CO 3 •- with both neutral and anionic molecules of SAs is single electron transfer reaction. Frontier molecular orbital theory (FMO) illustrated that deprotonation of the sulfonamide group of SAs decreases the charge density on the heterocyclic ring, facilitating the electrophilic addition of CO 3 •- . The second-order rate constants of the neutral and anionic molecules of SAs with CO 3 •- were calculated as 7.57 × 10 1 ∼1.84 × 10 8 and 1.81 × 10 7 ∼7.94 × 10 9 M -1 s -1 , respectively, resulting in an increase in the apparent reaction rate constants with pH. Stepwise multiple linear regression was employed to predict reactivity with anionic sulfonamide antibiotics (SAs - ). Two models with outstanding prediction and stability were developed with coefficients of determination R 2 of 0.660 and 0.681, respectively. The degradation kinetics simulation indicated that in the UV/H 2 O 2 process in the presence of carbonate, the degradation rate of SAs increased with pH. Furthermore, the contribution of CO 3 •- to SMX degradation increased while that of HO • decreased. This study highlights the contribution of carbonates to the micropollutant degradation in the UV/H 2 O 2 process as the model, providing theoretical insights into the development of carbonate-based AOPs.