Ni sintering is one of the main factors in SOFC degradation. In this study, we first investigated the surface orientation on Ni nanoparticles by using molecular dynamics (MD) method. It was identified that Ni nanoparticles mainly consist of four facets: (111), (100), (110), and (113). We also analyzed the stability of surface energy, which is the dominant driving force for the sintering phenomena, in various sizes of Ni nanoparticles. The MD simulation of two particles system was performed to investigate the sintering phenomena. We found that the diffusion coefficient is almost the same between 1373 and 1673 K, while contact surface orientation is different. It is indicated that dominant sintering mechanism of Ni nanoparticles is surface diffusion.