【Objective】Reactive oxygen species (ROS) at the soil-water interface play a crucial role in carbon/nitrogen cycling and pollutant transformation. However, it is still unclear how biochar influences the formation of ROS at the soil-water interface. Thus, this study aims to explore the formation behaviors and factors influencing ROS generation at the soil-water interface containing biochar. 【Method】Under simulated solar illumination conditions, the probe capture method was used to quantitatively analyze the generation kinetics and mechanisms of three typical ROS (hydroxyl radical ?OH, hydrogen peroxide H2O2, and superoxide radical (O2??) at the 10 gkg-1 biochar-amended soil-water interface. The effects of biochar pyrolysis temperature, dissolved biochar carbon (DBC), clay minerals (kaolinite), and dissolved organic matter (fulvic acid) on ROS formation were also examined at such interfaces. 【Result】The results showed that under light, substantial ?OH and H2O2 were generated at the biochar-containing soil-water interface, with concentration ranges of 0.43-0.83 μmolL-1 and 21.12-30.93 μmolL-1, respectively, which were 1.39-2.65 times and 1.31-1.91 times higher than those at the biochar-free interface (control group). In contrast, O2?? concentration was low (< 0.2 μmolL-1), significantly lower than that in the control. DBC played an important role in the formation of ROS, and after removing DBC, the generation of H2O2 in the water-soil interface containing biochar was significantly inhibited, but the generation of ?OH was not affected. Also, kaolinite significantly inhibited the capacity of biochar to mediate ROS generation at the soil-water interface under light (except for high-temperature biochar) and reduced the conversion efficiency of H2O2 to ?OH. Fulvic acid significantly enhanced H2O2 generation at the light-irradiated, biochar-containing soil-water interface but decreased ?OH concentration.【Conclusion】Light plays a critical role in mediating ROS formation at the biochar-amended interface: it not only promotes H2O2 generation and transformation, but also facilitates ?OH production and O2?? conversion. However, biochar-mediated ROS generation at the interface is not entirely dependent on light. The generation of ROS at the light-irradiated, biochar-amended soil-water interface is collectively determined by biochar surface persistent free radicals, oxygen-containing functional groups, as well as dissolved organic carbon and Fe2+ contents at the interface. These findings provide an important reference for understanding the formation and distribution of ROS in biochar-amended soils.