The mechanism of the oxygen evolution reaction over NiFe-layered double hydroxides is investigated using first-principles DFT + U calculations. We consider three possible reaction pathways for O-2 evolution. Our calculations show that O-2 evolution from the OH*-OH* species has high energy barrier and from OOH* species have a little high energy barrier. Finally, we discover that O-2 can easily release from OO* species. The mechanism of oxygen evolution reaction (OER) over NiFe-layered double hydroxides was investigated using DFT + U method by First-principle. The present work considered two possible reaction pathways for O-2 evolution. Our calculation suggested that O-2 evolution from the OOH* species may be more favorable because of advantages in energy profile, oxygen adsorption, and overall energy barrier. In addition, density of states (DOS) and partial density of states (PDOSs) of NiFe-LDH and Ni(OH)(2) showed that NiFe-LDH had a more stronger capability for electron transportation and higher activity than Ni(OH)(2). Additionally, it was found that Bader charge of Ni had a large fluctuation in the former elementary steps, while in the later that of Fe had. The research suggested that the transitional metal Fe/Ni-based hydrotalcite was a suitable material for OER, for not only they had great activity and stability, but also they were widely used and comparatively cheap. [GRAPHICS] .