Electrochemical reduction process is a promising method for wastewater treatment, and its performance is determined by cathode material. Nitrogen doped carbon is a kind of favorable cathode material for electrochemical reduction, but deep understanding for the effect of nitrogen concentration and reduction pathway is still needed. In this paper, nitrogen doped porous carbon (NPC) with different nitrogen concentration were fabricated by directly carbonization of ZIF-8 under various temperatures. The electrochemical reduction performance of NPCs was evaluated by reducing nitrobenzene (NB), and the effects of nitrogen concentration were discussed. NPC with 22.7% nitrogen concentration exhibited the best NB reduction performance with the NB removal constant about 1.0 h under optimal conditions; the NB removal rate and aniline (AN) production on this NPC are 4.2 and 8.5 times higher than graphite electrode. Further H* quenching experiment indicates the NPC electrochemical reduction process mainly following an indirect hydrogenation reduction pathway. These results offer some insights into the electrochemical reduction process on nitrogen doped carbon, which may facilitate the design of efficient metal free carbon based catalyst for wastewater electrochemical pretreatment.