Although metal sulfides have demonstrated exceptional catalytic properties in Fenton-like reactions, little is known about the role of sulfur species in transforming highly active species responsible for degradation organics. CuS (∼12 nm) nano-capsules embedded in the biochar (CuS-BC) were prepared from copper-rich biomass, which could activate H2O2 (4 mM) and completely remove tetracycline (TC) from water within 210 min. Compared with BC/H2O2/Vis system, the degradation efficiency of TC in the CuS-BC/H2O2/Vis system was improved by 14.8 times, and the utilization efficiency of H2O2 was improved by 86 times. The whole degradation process of TC can be divided into two stages: quasi-first-order reaction kinetics (kobs = 0.015 min−1) and zero-order reaction kinetics (kobs = 6.457 mol/L/min). Within 90 min, H2O2 is activated to produce hydroxyl radicals (OH) by surface Cu2+ on CuS and photogenerated electrons (e−) generated from CuS photoexcitation, which react immediately with surface SO32− to form SO4−. After 90 min, CuIII-peroxo species (CuIII-O22−-(SO32−)n) formed by electron transfer between CuI, O2, and surface SO32− oxidize the remaining 50 % TC through interface interaction. CuS-BC catalyst exhibits excellent photostability and suitability for actual antibiotic wastewater. Overall, this study offers mechanistic insight into the role of sulfur species in the sulfide-based Fenton reactions.