Abstract: With the purpose of uncovering the performance characteristics of three-dimensional biofilmelectrode 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 nir S-based clone library.Resultsshow that 3BER-S technology is superior to 3BER technology in TN removal efficiency and buffering p H. 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 andsulfur autotrophic denitrification process take account for a certain proportion.