An　innovative　nitrogen-doped　sludge-derived　biochar　(NSBC)　electro-Fenton　cathode　was　fabricated　by　a　hydrothermal　and　pyrolysis　combination　method,　which　was　applied　to　the　degradation　of　sulfamethoxazole　(SMX).　The　superficial　characteristics　of　the　optimal　cathode　(NSBC*@Ni-F)　showed　a　large　number　of　oxygen　reduction　reaction　(ORR)　electrocatalytic　active　sites　under　acidic　conditions　with　high　electrons　transfer　efficiency.　The　two　nitrogen　species　(pyridinic-N　and　graphite-N)　dominated　the　ORR　electrocatalytic　active　sites.　The　H2O2　yield　(195.99　mg　L-1)　and　corresponding　current　efficiency　(73.69　+/-　1.2%)　using　NSBC*@Ni-F　cathode　were　7　times　higher　than　that　of　bare　sludge　biochar　as　cathode　in　EF　system.　An　excellent　SMX　removal　efficiency　(95.72%)　was　achieved　as　well.　The　TOC　removal　achieved　85.11%　and　corresponding　energy　consumption　reached　as　low　as　12.03　kW　h　kg(-1).　Rational　reaction　intermediates　were　put　forward　during　EF　procedure　to　predict　and　explore　the　SMX　degradation　pathway　for　water　remediation.　This　study　is　hopeful　to　hew　out　a　new　road　to　develop　eco-friendliness　and　cost-effective　cathode　material　in　EF　system　with　adequate　activity　and　reuse　stabilization.