Developing highly active and stable electrocatalysts from earth-abundant elements are imperative for the large-scalable production of hydrogen. Herein, the three dimensional amorphous NiCoSxOy nanosheets arrays directly grow on Ni foam (NiCoSxOy NSs/NF) through a facile one-step electrodeposition is firstly reported. The special in-situ grown 3D nanosheets arrays, largely exposed active sites and enhanced electrical conductivity enable the resultant NiCoS0.14O3.25 NSs/NF to possess remarkable electrocatalytic performance and stability towards water splitting in 1 M KOH. Specifically, the introduction of S ligand into the hydroxides through a straightforward and convenient electrodeposition method boost the robust composition and comprehensive activity of the NiCoSxOy NSs. Such binder-free, easily prepared NiCoS0.14O3.25 NSs/NF electrode requires the overpotential of 250 mV and 170 mV at 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. When functionalizing as two identical cathode and anode in an alkaline electrolyzer, NiCoS0.14O3.25 NSs/NF displays the efficient and robust property on both OER and HER. Remarkably, serving as bifunctional electrode in alkaline electrolyzer, it only needs 1.64 V to reach the current density of 20 mA cm−2. This study provides a valuable guideline to synthesize non-noble and efficient bifunctional electrocatalysts using a time-saving but facile electrochemical method.