Modified　sludge　biochar,　recognized　for　its　notable　economic　and　environmental　benefits,　demonstrates　potential　as　an　effective　catalyst　for　peroxydisulfate　(PDS)　activation.　Nevertheless,　the　specific　mechanisms　underlying　its　catalytic　performance　require　more　comprehensive　investigation.　In　this　study,　a　modified　biochar　(TSBC)　doped　with　oxygen　(O)　and　nitrogen　(N)　atoms　was　synthesized　from　sewage　sludge　and　tannin　extract,　which　significantly　enhanced　the　activation　of　PDS　for　the　degradation　of　sulfamethoxazole　(SMX).　The　TSBC/PDS　system　demonstrated　robust　performance　for　SMX　degradation,　achieving　over　90%　efficiency　over　a　wide　pH　range　(3-10).　Subsequent　quenching　experiments　demonstrated　that　TSBC　predominantly　catalyzed　PDS　to　generate　O21,　which　effectively　degraded　SMX　via　a　non-radical　pathway.　The　O-　and　N-containing　functional　groups　in　TSBC　were　identified　as　the　primary　catalytic　sites.　Besides,　density　functional　theory　(DFT)　calculations　revealed　that　the　incorporation　of　graphitic　N　significantly　improved　the　adsorption　capacity　of　PDS　on　the　TSBC　surface.　Furthermore,　based　on　the　identification　of　intermediates　and　theoretical　calculations,　SMX　was　degraded　mainly　by　two　different　pathways:　S-N　cleavage　and　O21　oxidation.　This　study　offers　a　foundational　framework　for　the　targeted　modification　of　sludge　biochar,　thereby　expanding　its　applications.