The search for cost-effective and highly active transition-metal-based electrocatalysts is of great importance for overall water splitting to generate clean energy hydrogen. In this work, we present a controllable structural transformation engineering strategy to construct 3D hierarchical CoP porous microscale prism-like superstructure (assembled with nanoflakes) arrays grown on surface-phosphatized Ni foam (CoP/SPNF). Specifically, Zn/Co-based composite arrays with a nanowires@prism hierarchical structure were prepared on Ni foam first. Then, porous Co-based compound arrays with a nanoflakes@prism hierarchical structure were obtained through removing the Zn-based compound by alkaline etching. Finally, CoP arrays were produced through phosphatization of the prepared Co-based array precursor, using NaH2PO2 center dot H2O as the P source. The fabricated CoP/SPNF electrocatalyst exhibits impressive bifunctional performance for the hydrogen evolution reaction (HER, overpotential of 45 mV at 10 mA cm(-2)) and oxygen evolution reaction (OER, overpotential of 215 mV at 80 mA cm(-2)) and consequently enables efficient electrolytic water splitting with a low cell voltage of 1.547 V at 30 mA cm(-2) and a prominent durability. Versatile CoP with its porous superstructure arrays on surface-phosphatized Ni foam can increase the exposure of electrochemically active sites and render easy contact with the electrolyte, thus facilitating fast electron transport and effective electrolyte diffusion during the electrocatalytic process, as well as promoting the release of product gas bubbles from the electrode. This work provides an effective strategy for the design and preparation of non-noble-metal bifunctional electrocatalysts for overall water splitting electrolysis.