This study investigates the mitigation of S2- inhibition in the sulfur autotrophic denitrification and anammox coupling system through the preparation and structural characterization of g-C3N4. The results indicated that g-C3N4 demonstrated a substantial capacity to mitigate the inhibitory effect of S2- on the coupling system. The optimal dosage of 150 mg-L-1 led to an enhancement in NH4+-N removal by 30.27%-43.25%, and in TN removal by 1.21-1.33 times. The addition of g-C3N4 led to an acceleration in the conversion of S2-, reducing the S2- inhibition time. The cytochrome c content increased by 26.97% and ETSA by 116.67%. CV and Tafel plots showed an increase in system capacitance and exchange current density, which strengthened the electrochemical properties of the reaction system, reduced the electron transfer resistance. High-throughput sequencing analysis showed that the abundance of Planctomycetota increased from 3.37 to 7.54 % and the abundance of Candidatus_Brocadia increased from 0.99 to 1.26 % after the addition of g-C3N4, which provided a favorable guarantee for the efficiency of nitrogen removal in the coupled system.