The practical development of lithium–sulfur (Li–S) batteries is largely obstructed by their poor cycling stability due to the shuttling effect of soluble polysulfides. To address this issue, we herein report an interconnected porous N-doped carbon network (NPCN) incorporating Fe3C nanoparticles and Fe–Nxmoieties, which is used for separator modification. The NPCN can facilitate lithium ion and electron transport and localize polysulfides within the separator’s cathode side due to strong chemisorption; the Fe3C/Fe–Nxspecies also provides chemical adsorption to trap polysulfides and Fe3C catalyzes the redox conversion of polysulfides. More importantly, the catalysis effect of Fe3C is promoted by the presence of Fe–Nxcoordination sites as indicated by the enhanced redox current in cyclic voltammetry. Due to the above synergistic effects, the battery with the Fe3C/Fe–Nx@NPCN modified separator exhibits high capacity and good cycling performance: at a current density of 0.1C, it yields a high capacity of 1517 mAh g–1with 1.2 mg cm–2sulfur loading and only experiences a capacity decay rate of 0.034% per cycle after 500 cycles at 1C; it also delivers a good capacity of 683 mAh g–1at 0.1C with a high sulfur loading of 5.0 mg cm–2; after 200 cycles, the battery capacity can still reach 596 mAh g–1, corresponding to 87% capacity retention. Our work provides a new and effective strategy to achieve the catalytic conversion of polysulfide and is beneficial for the development of rechargeable Li–S batteries.