The practical deployment of lithium-sulfur (Li-S) batteries is impeded by severe polysulfide shuttle effects and sluggish redox kinetics. The use of heterostructures as catalysts in sulfur hosts is expected to improve the electrochemical performance of Li-S batteries. However, single heterostructures still suffer from the fatal problems of few active sites and high charge transfer barriers. Herein, defect-engineered MoO_2–x-Mo₂C@NC (NC is the abbreviation form of nitrogen-doped carbon) is designed as an efficient electrocatalyst to adjust the surface properties and electron distribution of the heterostructure by introducing a defective structure into the heterostructure, thereby enhance active site exposure. The d-orbitals of Mo₂C facilitate strong interactions with the p-electrons of MoO₂, enabling efficient electron transfer between reactants and active sites. DFT calculations confirm the interaction of the d orbitals of Mo₂C with the p electrons in the MoO₂ material, effectively lowering the reaction energy barrier. As a result, the S/MoO_2–x-Mo₂C@NC exhibits remarkable cycle stability, retaining a specific capacity of 714 mAh·g^–1 after 500 cycles at 0.5 C. This work provides insights into defect-driven heterostructure design for advanced Li-S batteries.