Although Ni₃N possesses superior hydrogen desorption behavior, its alkaline hydrogen evolution reaction (HER) catalysis is substantially hindered, due to the high-lying unoccupied orbital center induced sluggish water dissociation kinetics. Herein, we successfully endow Ni₃N with exceptional alkaline HER activity by in situ interfacial engineering. The prepared Ni₃N/MoO₂ interfacial system delivers an ultra-small overpotential of 21 mV at 10 mA cm⁻², which is very close to that of the benchmark Pt/C catalysts. Density functional theory (DFT) calculations reveal that MoO₂ with a lower unoccupied orbital center could substantially boost the water dissociation kinetics, while the hydrogen desorption proceeds on Ni₃N. The capability to understand and design interfacial systems provides an effective pathway for the rational construction of HER catalysts and beyond.