Platinum (Pt) remains the benchmark electrocatalyst for alkaline hydrogen evolution reaction (HER), but its industry-scale hydrogen production is severely hampered by the lack of well-designed durable Pt-based materials that can operate at ampere-level current densities. Herein, based on the original oxide layer and parallel convex structure on the surface of nickel foam (NF), a 3D quasi-parallel architecture consisting of dense Pt nanoparticles (NPs) immobilized oxygen vacancy-rich NiO heterojunctions (Pt/NiO-O) as an alkaline HER catalyst is developed. A combined experimental and theoretical studies manifest that anchoring Pt NPs on NiO-O leads to electron-rich Pt species with altered density of states (DOS) distribution, which can efficiently optimize the d-band center and the adsorption of reaction intermediates as well as enhance the water dissociation ability. The as-prepared catalyst exhibits extraordinary HER performance with a low overpotential of 19.4 mV at 10 mA cm, a mass activity 16.3-fold higher than that of 20% Pt/C, and a long durability of more than 100 h at 1000 mA cm. Furthermore, the assembled alkaline electrolyzer combined with NiFe-layered double hydroxide requires extremely low voltage of 1.776 V to attain 1000 mA cm, and can operate stably for more than 400 h, which is rarely achieved.