Developing cost-effective and high-performance bifunctional catalysts for overall water splitting is of enormous importance for the realization of sustainable clean-energy technologies. Herein, the unique Mo-O linkage enhanced CoP nanosheets supported on Ni foam (NF) and the systematical investigation of their performance for overall water splitting as a function of the composition are reported. The fine-tuning of Co/Mo ratios in the Co-Mo precursors realized by controlling the dosages of capping agent (urea), which enables CoO to grow along its (111) crystalline orientation and retard the incorporation of Mo-O. As a result, the optimized CoP/MOL/NF-10 exhibits the best hydrogen evolution reaction (HER) activity with low overpotentials (eta) of 87 mV at 10 mA cm(-2). DFT calculation confirmed the O-site on surface is more advantageous to the adsorption of H, when CoP with proper mounts of Mo-O linkages and giving rise to a decent Delta G(H) value. When the CoP/MOL/NF-10 employed as anode for OER, the current density of 20 mA cm(-2) is achieved at a low overpotential of 270 mV. In the end, a symmetric electrolyzer built by CoP/MOL/NF-10 deliveries a current density of 10 mA cm(-2) at a cell voltage of 1.52 V with excellent stability.