First-principles were used to investigate hydrogen adsorption and diffusion on clean and Al doped Mg2Ni(100) surfaces. The calculation results show that H prefers to adsorb onto Mg-Ni bridge sites and Mg-Mg bridge sites on a clean Mg2Ni(100) surface, and their adsorption energies range from1.19 to 1.52 eV. For the Al doped Mg2Ni(100) surface, H prefers to adsorb onto the Al-Ni, Mg-Ni, Mg-Al bridge sites and the adsorption energies range from 0.10 to 0.29 eV. The results indicate that the Al doped Mg2Ni(100) surface reduces the adsorption energy for hydrogen. The transition state calculation shows that the energy barrier for H that diffuses from the clean and the Al doped Mg2Ni(100) surface to the subsurface is 0.59 and -0.04 eV, respectively. Doping the Mg2Ni(100) surface with Al weakens the interaction between H and the surface, and also reduces the barrier for hydrogen diffusion, which may be one reason for improving the kinetic properties of hydrogen adsorption for Mg2Ni alloy doped with Al.