Abstract: In order to improve the nitrogen removal efficiency of three-dimension-electrode biofilm process,the effects of ρ(C)/ρ(N) on operation characteristics and denitrifying bacteria population community characteristics of a coupled 3-dimensional biofilm-electrode with sulfur autotrophic denitrification technology(3 DBER-S) were investigated at different ρ(C)/ρ(N) conditions.The operating result indicates that there is no significant impact of ρ(C)/ρ(N) on denitrification performance in 3BER-S.And the TN removal efficiency is more than 80%at different ρ(C)/ρ(N) conditions.Moreover,the effects of ρ(C)/ρ(N) on denitrifying bacteria population and denitrification nutrition types in 3BER-S system were found.At high ρ(C)/ρ(N) condition,there is less species of denitrifying bacteria in 3BER-S system,where the Thauera acts as the dominant bacteria and heterotrophic denitrification is the main process.When the ρ(C)/ρ(N) is reduced,both the denitrifying bacteria species and the proportion of sulfur autotrophic denitrification bacteria increase.In a word,the 3BER-S system maintains high and stable nitrogen removal efficiency at different ρ(C)/ρ(N) conditions,because the sulfur makes up for the deficiency of the denitrifying electronic donor in 3 BER-S at low ρ(C)/ρ(N)condition.