Efficient bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) play crucial roles in water electrolysis. However, the discrepancy in binding affinities of catalytic sites to O/H-contained intermediates makes it difficult to achieve OER and HER bifunctional catalysis simultaneously. Multi-component heterostructures have been demonstrated to be an effective solution to realize bifunctional electrocatalysts, but the division of labor and action mechanism of each component are not fully elucidated. Therefore, based on asymmetrical crystal field stabilization energy (CFSE) between NiS and Ni₂P, the heterogeneous catalyst (NiS/Ni₂P@NF) with built-in electric field (BEF) is constructed in this paper, which showed efficient bifocal water cracking. DFT calculation has confirmed that BEF causes the directional movement of electrons in the material, thus optimizing the OER/HER reaction path. Further control experiments indicated that NiS and Ni₂P serves as the active species for the corresponding OER and HER, thus NiS/Ni₂P@NF delivers a remarkably reduced cell voltage of 1.62 V (10 mA cm⁻²) within a H-type electrolyzer as both anode and cathode electrodes. The strategy of constructing BEF based on asymmetrical CFSE has the potential to precisely induce the local electron flow of the catalytic site and accurately design multifunctional catalysts with composition-function contrast.