Two kinds of Mg-based alloy nanoparticles Mg-Ni and Mg-Ni/La2O3 were prepared by the DC arc plasma discharge method, and the phase structure and the electrochemistry performances of Mg-Ni nanoparticles with rare earth oxide La2O3 superficial modification were studied. The results indicate that rare earth oxide La2O3 modification for Mg-Ni nanoparticles can effectively suppress MgO and Mg(OH)2 phases. After doping La2O3, the Mg-Ni nanoparticles’ electrochemical performances are obviously improved, and the anticorrosion performance and the electric discharge performance in the thick alkaline solution are enhanced.