With　the　purpose　of　uncovering　the　performance　characteristics　of　three-dimensional　biofilm-electrode　reactor　and　sulfur　autotrophic　coupled　denitrification　system　(3BER-S),　a　comparative　test　between　3BER-S　reactor　and　general　three-dimensional　biofilm-electrode　reactor　(3BER)　was　applied.　Furthermore,　the　diversity　of　denitrifying　bacteria　in　3BER-S　reactor　was　studied　to　reveal　its　denitrifying　mechanism　by　nirS-based　clone　library.　Results　show　that　3BER-S　technology　is　superior　to　3BER　technology　in　TN　removal　efficiency　and　buffering　pH.　The　Shannon-Weaver　index　and　Simpson　index　of　denitrifying　bacteria　in　the　3BER-S　reactor　is　2.436　and　0.894,　respectively.　All　the　denitrifying　bacteria　in　the　3BER-S　system　have　a　high　similarity　with　Beta　proteobacteria,　and　35　clones　(61.49%)　in　the　clone　library　share　a　relatively　high　similarity　with　Thauera;　Thiobacillus　denitrificans　occupy　a　proportion　of　3.5%;　and　11　clones　(19.29%)　share　similarity　with　Acidovorax.　This　illustrates　that　the　heterotrophic　denitrification　process　plays　a　dominant　role　in　the　denitrifying　process　of　the　3BER-S　system　when　the　organic　carbon　source　is　sufficient,　and　hydrogenotrophic　denitrification　process　and　sulfur　autotrophic　denitrification　process　take　account　for　a　certain　proportion.