Abstract: Metal selenides have become a research hotspot as anode materials for sodium-ion batteries (SIBs) owing to their high specific capacity and favorable redox properties. However, the large ionic radius of Na⁺ results in sluggish reaction kinetics and severe volume expansion during reversible intercalation/deintercalation, posing major obstacles to their practical application. Herein, we propose a synergistic strategy integrating spatial construction and interface engineering. Through a tannic acid (TA)-induced etching-coordination process followed by in situ selenization/carbonization evolution, a core-shell ZnSe/CoSe₂@C composite featuring a nitrogen-doped carbon skeleton and bimetallic heterojunction components is successfully constructed. Moreover, the key influence of the metal composition ratio on the sodium storage behavior is systematically investigated. In this composite, the carbon-based skeleton forms a core-shell architecture with internal cavities, establishing continuous electron transport pathways and providing buffering space for volume expansion. Meanwhile, the heterointerface between ZnSe and CoSe₂ generates a built-in electric field, which modulates charge distribution and reduces the Na⁺ diffusion barrier, thereby accelerating reaction kinetics. Benefiting from the synergistic effects of structure and composition, the optimized ZnSe/CoSe₂@C(1∶2) electrode exhibits superior sodium storage performance, achieving a reversible specific capacity of 737.3 mAh·g⁻¹ after 100 cycles at 0.1 A·g⁻¹. Moreover, it retains a reversible specific capacity of 319.6 mAh·g⁻¹ even after 400 cycles at a high current density of 1 A·g⁻¹. This work elucidates the synergistic sodium storage mechanism combining heterointerface field effects and structural confinement, providing valuable design insights for the development of application-oriented metal selenide anodes.