The impact of HCO3- on the photodegradation of β-blockers was investigated under simulated sunlight irradiation. The mechanism of the effect of HCO3- on the photodegradation of β-blockers was revealed. And the degradation products of β-blockers were identified, the possible degradation pathways were proposed. The results showed that the photodegradation rate of sotalol (SOT) increased significantly in the presence of HCO3-, but had no effect on the degradation of carvedilol and arotinolol. Quenching experiments show that carbonate radical (CO3·-) is formed by the direct oxidation of HCO3- by triple-excited SOT (3SOT*), and plays an important role in the photodegradation of SOT. Electron paramagnetic resonance spectroscopy and determination of degradation products further prove the formation of CO3·- in the presence of both SOT and HCO3-. Competitive kinetics experiments show that the three β-blockers have high second-order rate constants (107-108 m-1 s-1) for the reaction with CO3·-. However, only 3SOT* has a high reduction potential that could oxidize HCO3- to produce CO3·-. Therefore, the enhancement effects of HCO3- on the photodegradation of SOT was observed in the system. In addition, Seawater DOM and freshwater DOM exhibit different roles in HCO3--induced photochemical transformation of SOT. The results show that DOM derived from seawater can increase the photodegradation rate of SOT induced by HCO3-, while SRNOM mainly acts as CO3·- quencher and reduces the removal rate of SOT in HCO3- solution. These results emphasize the important role of HCO3- in limiting the persistence of organic pollutants such as SOT in natural waters under sunlit natural waters, and especially in marine and coastal waters.