Molecular dynamic (MD) provided an ab initio simulation for nano-scale mechanical behavior of materials, provided that the inter-atomic potential is accurately prescribed. MD is particularly suitable in simulating the formation, the deformation, and the evolution of nanocrystals under a fast strain rate. To tackle large scale system and nano-seconds time duration, parallel algorithm is desired. The present paper reviews the recent advances in MD simulation for nanocrystals with attention focused on the applications toward nanomechanics. The examined issues are: formation of nanocrystalline metals, nanoindentation on nanocrystals, fast deformation of nanocrystals, orderdisorder transition, and nano-particle impact.