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The active sites and charge/mass transfer properties in electrocatalysts play vital roles in kinetics and thermodynamics of electrocatalysis, and impose direct impacts on electrocatalytic performance, which cannot be achieved by a simplex structure. As a prototype, the authors propose a double-heterojunctional nanostructure of NiS<sub>2</sub> /Ni<sub>3</sub> C@C containing NiS<sub>2</sub> /Ni<sub>3</sub> C and Ni<sub>3</sub> C/C heterojunctions as a general model to optimize the above issues and boost electrocatalytic performance. During the thermal reorganization, the in situ reaction between NiS<sub>2</sub> nanoparticles and carbon induces the formation of Ni<sub>3</sub> C between them and constructs tightly contacted two kinds of interfaces among the three components. The TEM and XPS reveal the intimately contacted three components and the as-constructed interacted dual interfaces, further confirming the formation of a porous double-heterojunctional nanostructure. Theoretical calculations uncover that the electron density redistribution occurs at Ni<sub>3</sub> C/C interface by spontaneous electron transfer from defected carbon to Ni<sub>3</sub> C and lower ΔG<sub>H*</sub> achieves at NiS<sub>2</sub> /Ni<sub>3</sub> C interface by the concentrated interfacial charge density, which favors the simultaneous realization of high catalytic activity and rapid charge/mass transfer. When applied for hydrogen evolution reaction (HER), the porous double-heterojunctional NiS<sub>2</sub> /Ni<sub>3</sub> C@C exhibits excellent HER activity and durability among all pH values. Profoundly, this special double-heterojunctional structure can provide a new model for high-performance electrocatalysts and beyond.