Abstract: The hydrogenation mechanisms of N₂ reduction reaction (NRR) on Ti₂CT₂ and Ti₃C₂T₂ (T=O* or OH*) MXenes are studied by first-principles study. And the DOS of N₂ adsorption, the Gibbs free energy of the reaction intermediate structure (ΔG), charge density difference(CDD), work function and activation energies (E_a) are calculated to explore the new mechanism of NRR reaction on the surface of OH * terminal MXene. The results show that N₂ undergoes physical adsorption on Ti₂CO₂ and Ti₃C₂O₂ surfaces (∆q≈0 e), while chemical adsorption occurs on Ti₂C(OH)₂ and Ti₃C₂(OH)₂ surfaces (∆q>0.2 e), Ti₂CO₂ and Ti₃C₂O₂ are do not favor NRR due to high η_NRR. While Ti₂C(OH)₂ and Ti₃C₂(OH)₂ can catalyze NRR by donating their surface H at initial steps and then via enzymatic mechanism, with the corresponding η_NRR of 0.29 V and 0.38 V, respectively. Moreover, the calculated η_NRR can be used as a function of φ: η_NRR=0.44φ−0.71, where the correlation coefficient (R²) is 0.97, showing a strong linear relationship between overpotential and work function. The strength and hybridization energy level of the N 2p orbitals and O 2p orbitals on Ti_n+1C_nT₂ and Ti_n+1C_n(OH)₂ are different during NRR, and delivering different catalytic activity for NRR. Finally, it concluded that the N₂ adsorption on Ti₂C(OH)₂ and Ti₃C₂(OH)₂ may via “N₂+2*H=*N₂H₂” at initial steps and then along enzymatic hydrogenation mechanism.