The P-based electrode electrocatalysts have exhibited high activities for the hydrogen evolution reaction (HER), but their structural stabilities in the long-term operation of water electrolysis pose a technical challenge for industrial-scale applications. In this study, amorphous NiP sheet arrays with rich active sites were created on nickel foam (NF) by in situ phase reconstruction, and then NiO ultrafine particles were generated within the NiP sheets. The array electrode exhibited not only enhanced catalytic activity verified by 76 mV of HER for NiO@NiP/NF at 10 mA cm-2, but also excellent structural stability in 1 M KOH solution proved by the fact that the structure of the assembled electrode remained intact after long-term operation at 100 mA cm-2 for 120 h.