In　this　study,　a　graphite　felt　(GF)　electrode　material　supporting　a　Cu-based　catalyst　(CuHDC-400/GF)　was　prepared　by　a　hydrothermal　process　and　subsequent　heat　treatment.　A　heterogeneous　electro-Fenton　(EF)　system　was　built　to　investigate　the　degradation　of　sulfamethoxazole　(SMX)　by　the　composite　cathode.　Scanning　electron　microscopy,　X-ray　diffraction,　Raman　spectroscopy,　and　X-ray　photoelectron　spectroscopy　were　used　to　characterize　the　physical　and　chemical　properties　of　the　composite　cathode.　The　results　show　that　the　composite　cathode　CuHDC-400/GF　has　excellent　catalytic　performance,　achieving　100　%　removal　of　SMX　(10　mg/L)　within　45　min　(aeration　rate　=　0.6　L　min−1,　current　density　=　5　mA　cm−2,　initial　pH　=　5.6).　Furthermore,　efficient　removal　of　SMX　can　be　achieved　over　a　wide　pH　range　(pH　=　3–9).　The　electrode　material　can　still　efficiently　degrade　SMX　after　eight　cycles.　Compared　with　a　heterogeneous　EF　system,　in　which　the　Cu　catalyst　was　directly　added　to　the　reaction　solution,　using　CuHDC-400/GF　as　the　cathode　realizes　the　in-situ　catalysis　of　H2O2,　leading　to　reduced　catalyst　consumption　and　enhanced　electrode　stability.　The　investigation　of　potential　SMX　degradation　pathways　and　mechanisms　revealed　that　the　continuous　production　of　active　free　radicals　is　facilitated　by　the　redox　cycle　between　CuⅠ　and　CuⅡ　on　the　electrode　surface,　which　can　enable　SMX　degradation.　Unlike　the　Fe-based　Fenton　reaction,　the　active　superoxide　radical　[rad]O2–　was　identified　as　the　major　contributor　to　SMX　degradation　in　this　system,　followed　by　the　hydroxyl　radical　[rad]OH.　The　active　sites　for　SMX　degradation　were　predicted　by　density　functional　theory　calculations.　Combined　with　the　measured　mass/charge　ratios,　the　possible　degradation　paths　and　intermediates　of　SMX　were　predicted.　Furthermore,　toxicity　analysis　shows　that　toxicity　significantly　declines　after　degradation.　This　work　is　expected　to　inspire　subsequent　research　on　heterogeneous　EF　cathode　materials　with　high　catalytic　performance.　©　2023　Elsevier　B.V.