Display omitted •Double single atoms FeMo@CoNi-OH/Ni3S2 is obtained by in situ epitaxial growth.•FeMo@CoNi-OH/Ni3S2 shows high activity to HER in wide pH range and OER in alkaline.•Different electronegativity of Fe and Mo leads to charge rearrangement in catalyst.•The synergies between Fe and Mo enhances OWS performance of FeMo@CoNi-OH/Ni3S2. The limitations of single-atom catalysts (SACs) hinder their application in wide-pH range of hydrogen evolution reaction (HER) and overall water-splitting in alkaline solution. Herein, we fabricate a rod-like Ni3S2 material wrapped by single-atom Fe-Mo co-modified CoNi-based nanosheets (FeMo@CoNi-OH/Ni3S2). The introduction of Fe-SAs and Mo-SAs into CoNi-hydroxyl compounds effectively changes their electronic structure and enhances their conductivity, thereby improving HER and OER performance. FeMo@CoNi-OH/Ni3S2 catalyst endows HER with overpotentials of 89, 176 and 177 mV in alkaline, acidic and neutral solutions, respectively, as well as good oxygen evolution reaction (OER) performance with 160 mV in alkaline to achieve 10 mA cm−2. The combination of the experiments and theoretical calculations reveals that the synergistic effect of Mo-SAs with Fe-SAs effectively reduces the intermediate energy barrier of the water dissociation step. This work contributes to the understanding of the catalytic mechanisms of dual single-atomic active sites in HER and OER processes.