Hydrogen evolution reaction (HER) is one of the key components for the hydrogen-centered renewable clean energy system. Developing efficient HER electrocatalysts that make use of earth-abundant elements is highly desirable yet challenging. Herein, we report a three-dimensional (3-D) CoP3 nanoplate arrays in situ grown on carbon cloth (CoP3 NPAs/CC), which is synthesized by a facile topotactic phosphidation method under hydrothermal condition. As a HER electrocatalyst, the as-prepared CoP3 NPAs/CC exhibit great catalytic activity that is comparable to Pt, over a large pH range of 0-14. At pH = 0, such flexible and efficient CoP3 electrocatalysts can deliver a high current density of 100 mA cm(-2) at an overpotential as low as 113 mV, with no apparent activity loss over 40 h. By theoretical calculation and experimental measurements, the outstanding HER performance of the CoP3 NPAs/CC can be attributed to the good conductivity property, synergistic effect between Co and P, unique rich-phosphorous CoP3 nanoplate arrays structure and the great intrinsic catalytic activity. As a highly efficient HER catalyst, CoP3 NPA offers a promising alternative of non-PGM catalysts for electrochemical hydrogen production.