Developing highly efficient and low-cost noble metal-free catalysts toward hydrogen evolution from water splitting is an attractive alternative strategy to solve the ever-increasing environmental contamination and energy demand. Herein, a porous CoP electrocatalyst with a concave polyhedron (CPH) structure was facilely prepared by a topological conversion strategy using Co-MOF (ZIF-67) polyhedrons as the precursor. The morphology of Co-MOFs is well inherited by the as-prepared CoP sample due to the multi-step calcination process at low temperature, which results in the formation of a porous structure. Compared with the contrastive CoP nanoparticles (NPs), the obtained porous CoP CPH electrocatalyst exhibits a remarkably enhanced electrocatalytic performance with a current density of 10 mA cm−2 at an overpotential of 133 mV and a superior durability for the hydrogen evolution reaction (HER) in acid media. A small Tafel slope of ca. 51 mV dec−1 reveals a Volmer–Heyrovsky mechanism during the HER. This work provided a new insight to fabricate morphology-controlled transition metal phosphides with a porous structure via topological conversion, which have importantly potential applications, such as electrocatalysis, photocatalysis and sensors, thanks to their porosity and controllability.